The given curve is rotated about they-axis. Find the area of the resulting surface.

0 ≤x≤ 4

can someone help me figure this out. I know what the answer is i just dont know how to come to it. I found dy=(1/2)x-(1/2x)dx and then took dy/dx=2pi(x)*sqrt(dx^2+dy^2) and solved...any help? my way got me a completely wrong answer