How to write words to match the math expression

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?

Fast! find the length of cu. the triangles are similar. show your work.

The result of which expression will best estimate the actual product of (-4/5) x (3/5) x (-6/7) x (5/6) (i need an expression not an answer)