Problem #7: A large tank contains 120 litres of water in which 24 grams of salt is dissolved. Brine containing 11 grams of salt per litre is pumped into the tank at a rate of 8 litres per minute. The well mixed solution is pumped out of the tank at a rate of 2 litres per minute. (a) Find an expression for the amount of water in the tank after t minutes. (b) Let x() be the amount of salt in the tank after t minutes. Which of the following is a differential equation for x(t)? Enter your answer as a symbolic Problem #7(a): function of t, as in these examples (A) = 16 - 8 x(0) (B) = 88 - 2 x(1) (C) dx = 8 8 x(1) (D) = 8 - x(t) at 120 + 8t 120 + 6t 120 + 6t at 60 2 x(t) (E) dx = 16 - - 1x(t) (F) ax 2 x(t) = 88 - X(0 (H) adx = 8 -. at 60 = 16 - 120 + 8t (G) at 120 + 8t (I) = 88 8 x(t) 120 + 6t