Atank contains 400 l of fluid in which 50 g of salt is dissolved. brine containing 2 grams of salt per liter is pumped into the tank at a rate of 5 l/min. the well-mixed solution is pumped out at the same rate. (a) find the number aſt) of grams of salt in the tank at time t. (b) what is the concentration c(t) of the salt in the tank at time t? (c) at what time is the concentration of the salt in the tank two times the initial concentration?