6· [10pts] a 300-gal tank initially contains 100 gal of brine containing 30 lbs of salt. brine containing 1 lb of salt per gallon enters the tank at the rate of 6 gal/s, and the well-mixed brine in the tank flows out at the rate of 4 gal/s. how much salt will the tank contain when it is full of brine? it's the question about elementary differential equation. provide specific solution and explanation with clear handwriting.