The slope of a line is the rate that a line increases or decreases. The question tells us that Matt looked at the relationship between age, in years; thus, the correct answer should include "each year", which eliminates the answer choices that include "each month". Finally the slope is , which is a positive number; thus, the line increases by  each year. This means that the correct answer is "Each year, a person's salary increases by ". 

The equation of the best fit line will be in slope intercept form:

The question tells us that the slope is  and we are provided with a data point, so we can plug in the known values into the equation to solve for the  

We had to convert our percentage into a decimal in order to multiple, but we need to change it back to a percent before we subtract so that we arrive at the correct answer because  is a percent based on the information from the question

 which means the y-intercept is 

We know, from attending school ourselves, that every day we learn something new in school. When a day of school is missed, there is a lot of catch up that needs to be done, but the teacher's instructions and lesson given each day can't be repeated the day you return, because the teacher has to move on with the rest of the class. If you missed a week of school, that's five days of lessons that were missed. Wouldn't it be challenging to catch up on what was missed, as well as learning what the teacher is currently teaching when you return? This would likely be challenging; thus, we can conclude that the more days of school missed, the lower a students final grade will be. As the number of days missed increases, the final grade will decrease; thus, the best fit line will have a negative slope. 

To help us answer this question, let's think about what we know about jobs:

If you were to get a part time job when you turn , it's likely that you'll make minimum wage because it's your first job and you haven't finished high school, nor would you have a college education. However, if you think about a doctor, graduating from medical school when he/she is about  years old, the doctor is likely going to make a lot more than minimum wage because he's gone through high school, college, and medical school. As you can probably assume, doctors make a salary much higher than minimum wage. Based on this scenario, we can conclude that as age increases, salary increases; thus, the slope of the best fit line will have a positive slope. 

We know, from attending school ourselves, that completing homework assignments and studying for quizzes and tests means that we will do better in school than if we didn't do those things. Completing homework and studying for tests takes time outside of school. Normally, the harder you study and the more time you spend studying, the more likely you are to do well in school. If you don't study at all, nor spend anytime completing homework assignments, your school grade will likely be lower than if you had spent time preparing and completing assignments; thus, we can conclude that the more time we spend studying, the higher our  will be. As the number of hours studied increases, the  will increase; thus, the best fit line will have a positive slope. 

We know, from attending school ourselves, that when we have a test coming up that we want to do well on, we'll study for the test. Normally, the harder you study and the more time you spend studying, the more likely you are to do well on the test. If you don't study at all, and don't know the material that's being covered on a test, you'll like do poorly on a test; thus, we can conclude that the more time we spend studying, the higher our test grade will be. As the number of hours studied increases, the score on the test will increase; thus, the best fit line will have a positive slope. 

The question tells us that age is the independent variable, or the , and height is the dependent variable, or the 

The  is when ; thus, when a person is just born their age is  and their average height is 

The question tells us that age is the independent variable, or the , and price is the dependent variable, or the 

The  is when ; thus, when a car is brand new its age is  and the average price is 

Imagine that you were buying a car. You have two options: a brand new car for  or the same car, but a ten year older model for , which one would you pick? Most likely, you would take the brand new car because they are the same price. As a car get's older, it decreases in value because it becomes outdated and it the car will likely have been driven a lot more miles the older it gets. This means that the slope of the best fit line will be negative, since the price will decrease as the age increases. 

Let's think about ourselves in this scenario, as you've gotten taller, has your weight increased or decreased? Most likely, as your height has increased your weight has also increased; thus the slope of the best fit line for this data would be positive.