integral calculus pls help me

Question

volume y=x, y=x, about x=4

Answer 1

Use the expression V=π∫₀⁴(4-y)²dy this gives π∫₀⁴(16-8y + y²)dy. Doing the integration gives π( 16y -4y² + y³/3)₀⁴. This gives π(64 -64 +64/3) which gives V= 64π/3