these are just two semi-circles, one with a diameter of 22 and the other with a diameter of 30 - 22, or 8, and therefore their radius are 11 and 4 respectively.

Yes that is extremely accurate
8/10 = 0.8
Therefore, 0.8 (8/10) is put on the number line shown below.
350 / 28 = 12.5 gallons, so 13 gallons needed
13 X 2.5 = $32.50