The length of a side of a rectangle is 2 units less than a number, and the width is 4 units more than the length. which of the following expressions represents the area of the rectangle, in square units?

Let's find the expressions for the length and width of the rectangle. The length (which we will call l) is 2 units less than some undefined number, thus we will use the variable x:
l = x - 2

The width is 4 more than this length:
w = l + 4 = (x - 2) + 4 = x + 2

Now, given that we have the length and width and are looking for the area, we need to multiply these expressions together.

One way to write this would simply be (x + 2)(x - 2). If we wanted to find a different way of writing the area, we could use FOIL to find all terms and get x^2 - 4.