Question about Volume of Solids

[Gauss177]

I'm having trouble with problems where you have to find the volume of a solids that are not solids of revolution. Can someone help me with these problems and also tell me a general way of approaching these problems? Thanks

Homework Statement

A hole of radius r is bored through the center of a sphere of radius R > r. Find the volume of the remaining portion of the sphere.

2. Homework Statement
The base of S (the solid) is an elliptical region with boundary curve $$9x^2 + 4y^2 = 36$$. Cross-sections perpendicular to the x-axis are isosceles right triangles with hypotenuse in the base.

 

[StatusX]

For 1, that is a solid of revolution, try drawing it. For 2, it is very similar to integrating solid of revolution, only instead of adding up circles you are adding up triangles. Again, if you can picture the shape it shouldn't be too hard.