Thanks sooo much Alec, you've been a great help... i have two more questions if you could possibly help me on these, I'd forever be in your debt.

The first question:

finding the volume obtained by rotating it the same area bounded by f(x)=10ln(x) and g(x)=4-(x^4)-x around the y-axis.

the second question:

the region in the first quadrant bounded by the coordinate axes and the graph of h(x)=15-2x^2 is revolved to form a solid. Use leftsum and evalf to approximate the volume of this solid by summing the volumes of 20, 40,200 and 500 disks of equal thickness. Then repeat with rightsum