A tank initially holds 100gal of a brine solution containing 20 lb of salt. At t=0 another brine solution containing 1lb of salt per gallon is poured into the tank at the rate of 3gal/min, while the well-stirred mixture leaves the tank at the same rate. Find the amount of salt in the tank at any time t.

Any help on this problem will be appreciated,

Cheers.