To find 5/12-3/8, you have to find a common denominator. A common denominator of 12 and 8 could be 24. So, you multiply 5/12, both the numerator and the denominator by 2, which gives you 10/24. Then, you multiply 3/8 both by 3 to get the common denominator of 24. 3/8x 3 is 9/24. So, 10/24-9/24 is 1/24 because you only subtract the numerator and keep the denominator the same.
Divide the volume of the tank (10,000 gallons) by the filling rate of 250 gallons/minute and you will Hours = hr x min x 3785 ml x 55 gal = 208175 = 115.6 hrs.
