Remove grouping signs −25+(32−18)+[−3(23−15)+5(10−12)] plz, how is it done? step by step

Ineed to learn how to solve 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?

Ithink i know it but i want to be sure so can you me out ?