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?