A tank initially contains 100 L of pure water. Brine containing 2 g/L of salt flows into the tank at 5 L/min, and the well-stirred mixture flows out at the same rate. Let S(t) denote the amount of salt (in grams) in the tank after t minutes.
Which expression gives S(t)?
a) 200e−0.05t
b) 200+200e−0.05t
c) 200(1−e−0.05t)
d) 200(1−e−0.2t)