given diameter: d = 23.5 cm
find radius: r = 23.5/2 = 11.75 cm
find volume: V = (4/3)πr³ = (4/3)π(11.75 cm)³ = 6795.2 cm³
divide volume by rate: 6795.2/230 = 29.24
even though 29.24 rounds down to 29, I'd say 30 pumps just to get over the volume given in the question. It can go either way on that. It's pretty messed up for them to choose numbers so close together