When Calvin put up feet of molding, he figured out the perimeter of the room was feet.  Since he knows that all four walls are the same width, he can use the equation to determine the length of each side by plugging in for and solving for .

In order to solve for , Calvin must divide both sides by four.

The left-hand side simplifies to:

The right-hand side simplifies to:

Now, Calvin knows the width of each room is feet.  Next he must find the area of each wall. To do this, he must multiply the width by the height because the area of a rectangle is found using the equation . Since Calvin now knows that the width of each wall is feet and that the height of each wall is also feet, he can multiply the two together to find the area.

Since Calvin wants to find how much paint he needs to cover three walls, he must first find out how many square feet he is covering.  If one wall is square feet, he must multiply that by .

Calvin is painting square feet. If one can of paint covers 24 square feet, he must divide the total space ( square feet) by .

Calvin will need cans of paint.

We can actually solve this by comparing volumes; the cube with the greater volume has the greater sidelength and, subsequently, the greater surface area.

The volume of the cube in (b) is the cube of 90 millimeters, or 9 centimeters. This is , which is greater than . The cube in (b) has the greater volume, sidelength, and, most importantly, surface area.

A square has four sides of the same length. 

One yard is equal to 36 inches, so each side of the square has length

 inches.

Its area is the square of the sidelength, or 

 square inches.

100 centimeters are equal to one meter, so 3,900 centimeters are equal to 

 meters. 

A square has four sides of the same length. Since the sum of the lengths of three of the congruent sides is 3,900 centimeters, or 39 meters, each side measures

 meters.

The area of the square is the square of the sidelength, or

 square meters.

The area of a square is the square of its side length:

Using the side length from the question:

However, it is impossible to tell with certainty which of  and  is greater.

For example, if , 

and 

so  if .

But if ,

and

so  if .

The area formula for a square is length times width. Keep in mind that all of a square's sides are equal.

So, if one side of a square equals 5, all of the other sides must also equal 5. You will find the area of the square by multiplying two of its sides:

A square plot of land with perimeter one mile has as its sidelength one fourth of this, or  mile; its area is the square of this, or 

 square miles.

One square mile is equivalent to 640 acres, so  square miles is equivalent to 

 acres.

This makes (b) greater.

One kilometer is equal to 1,000 meters, so divide each dimension of the plot in meters by 1,000 to convert to kilometers:

 kilometers

 kilometers

Multiply the dimensions to get the area in square kilometers:

 square kilometers

Since one square kilometer is equal to 100 hectares, multiply this by 100 to convert to hectares:

 hectares

This makes (a) the greater.