Question 1158329
1728 in^3/ft^3 (12*12*12)
so 680 in^3/sec*150 sec/2.5 min*1 ft^3/1728 in^3=59.03 or 59 ft^3


rough check. 
about 2.5 sec for 1 ft^3 of air
150sec/2.5 ft^3/sec=60 ft^3