Calculate the volume of the solid obtained when the triangle with vertices (2,5), (6,1) , (4,4) is rotated about the line x=-3 using either cylindrical shells or disks.

I found the slope for each line, and found an equation fro each. Then, using cylindrical shells with radius x+3, I found the volume generated by each line and then subtracted the results. However, I got a negative value.