Since you haven't provided the ,measurements, I'll just tell you how to solve this problem and you can apply using the measurements given in the problem.
I'll assume that the rectangular-shaped garage has a measurement x feet by y feet.
Now, we are given that the area of the rectangle is calculated using the following rule: Area = length * width
Assuming that "x" is the length and "y" is the width (or vice-versa), substitute with them in the given formula to get the area as follows: Area = x*y ft^2