Let R be the region bounded by the following curves. Use the disk or washer method to find the volume of the solid generated when R is revolved about he y-axis.
y=x, y=3x, y=12
Answer: $$\int_0^16 15/16 π$y^2$
This is setting up the integral only. 0, 16 were given in the graph. I followed the formula but I'm lost. Anyone can help so I can compare to my work and see what I've missed?