The sides of the rectangle are 5 to 8, its perimeter is 39. Find the area of the rectangle.

1. Let the length of one part be equal to c, then compose the expression for the perimeter of the rectangle:

2 * 5s + 2 * 8s = 39,

10s + 16s = 39.

26s = 39,

c = 1.5.

2. Find the sides of the rectangle, multiply the length of one part by the number of parts corresponding to each side:

1 side = 1.5 * 5 = 7.5,

2 side = 1.5 * 8 = 12.

3. Find the area by multiplying one side by the other:

Area = 12 * 7.5 = 90 units 2.

Answer: the area of the rectangle is 90 units2.