Combine the like terms to create an equivalent expression: −5r+8r+5

Ineed in figuring out this problem.

The volume of gas a balloon can hold varies directly as the cube of its radius. imagine a balloon with a radius of 3 inches can hold 81 cubic inches of gas. how many cubic inches of gas must be released to reduce the radius down to 2 inches?

What is the measure of ac? 5 units 13 units 26 units 39 units 3x- 2b 6x + 9