A tank contains initially (150) liter of brine in which (60)N of salt is dissolved starting at the
time (t=0), brine containing (2N/liter) of salt runs into the tank at the rate of (6 liter/min) and
the mixture, assumed to be kept uniform by stirring, runs out at the rate of (3 liter/min) as
shown in figure(1). Assuming that the tank is sufficiently large to avoid overflow, find the
amount of salt in the tank as a function of time. How much salt is in the tank at the end of
(5) min?