50-gallon barrel is filled completely with pure water. Salt water with a concentration of 0.3 pounds/gallon is then pumped into the barrel, and the resulting mixture overflows at the same rate. The amount of salt (in pounds) in the barrel at time t (in minutes) is given by Q(t) = 15(1 − e−kt) where k > 0. (a) Find k if there are 13.5 pounds of salt in the barrel after 50 minutes. Round your answer to 4 decimal places. k ≈ . (b) What happens to the amount of salt in the barrel as t → [infinity] ?