Urgent!!! disk and washer method

I can't get these 4 problems. I just don't get how to do them. I had a sub today in math and my teacher had us learn the chapter ourselves and do it but i can't get these answers. Help w/ explaining would highly be appreciated!!! I don't care if you only do one or two, i just need to grasp the subject. 1. find the volume of the solid bounded by these equations about the indicated lines. equations: y=square root of (x) y=0 x=4. About the line x=6. 2. sames as above: equations y=2x^2 y=0 x=2 about the line y=8.

3. same above : y=6-x y=0 y=4 x=0 about the line x=6.

4. y=x * square root of (4-x^2) about y=0.

Please Hurry!!! thanks in advance and i will be waiting here trying to figure them out Thanks!!

If you are going to do it

without the shell method you have to solve the equation so that it is no longer a function of x but now a function of y and use v=pi*$\displaystyle \int_c^d{R(y)^2}dy$