What is the volume? 30 inch diameter and 5 feet tall.

i get 24.54369 cubic feet and 183.59 gallons. this is correct right?

i ask this because this question seems wrong unless i round up..

here is the question

a flow rate of rate of 85 gpm enters a circular tank that is 30 inches in diameter and
5 feet tall, and then overflows out. calculate the detention time in minutes.

answers to choose from
(1) 2.2
(2) 5.2
(3) 10.4
(4) 15.5

well to find this we volume / flow

183.59 / 85 = 2.15 gpm

if we look at (1) 2.2 and we times that by 85 we get the volume should be 187. this question seems wrong unless i round up. what are your thoughts? is the question wrong unless we round up? what are your thoughts?