HCU MCA 2016 Paper

A 120 gallon tank initially contains 90 lb of salt dissolved in 90 gallons of water. Solution containing 2 lb/gallon of salf flows into the tank at the rate of 4 gallons/min and the well –stirred mix- true flow out of the tank at the rate of 3 gallons/min. A differential equation for the amount x(in lb) of salt in the tank is;