The area of a rectangle is length times width. So, there are two numbers for each set. The total area is 80 square inches. This is a case of finding factors for the number 80. A factor is a number that divides another number with no remainder. List all the factors.
These are the only sets that can create 80 square inches.
However, the last five sets are the same as top five sets in reverse order. So, the conclusion must be that there are five unique rectangles that can fit inside a rectangle of 80 square inches.