So, if you are trying to find the area of a sheet of paper that is 9 inches by 11 inches, and the unit square you want is the square inch, then there are 9 X 11 = 99 square inches in that sheet of paper. In this 4 inch by 3 inch rectangle,
each little square is a square inch. Count the little one-inch squares and find the total area. Is it the same as multiplying the width of the rectangle by the height?
Here are the formulas for the area of some common plane figures: