What your looking for is called the annulus (or the difference of two concentric circles). You can find the annulus by subtracting the area of the inner circle from the area of the outer circle. Volume of a circle= πr²
You are given the diameter in these problems, so you need radius.
For the first circle (8 in one) :
8/2=4 r=4
A=3.14(4)²
A=50.24
For the second one (10 in one) :
10/2=5 r=5
A=3.14(5)²
A=78.5
To find the measure of the annulus, you subtract those numbers, getting 28.26
