Expand 2x(8x+5)
This is something required for me to learn and I havent got a clue

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?

Which is f(5) for the function –2x2 + 2x - 3?

I’m really confused and need your assist me with this question i’ve never been taught