The radius is the distance from the center to any point. The distance from (2,1) to (0,1) is of course 2. The general formula for a circle with radius r and center (a,b) is

In our case we get
97.2 miles just multiply
5.4
18
_____
97.2 Remember, if there is a number behind the decimal point make sure to put a decimal point behind it in the answer
1/2 of 40= 20
40/5=8
20+8=28
28 of your CDs will not work properly.
I hope this helps!