(1 point) a tank contains 90 kg of salt and 2000 l of water. pure water enters a tank at the rate 8 l/min. the solution mixed and drains from the tank at the rate 4 l/min. (a) write an initial value problem for the amount of salt, y, in kilograms, at time t in minutes dy (kg/min) y(0)= kg. dt (b) solve the initial value proble m in part (a) y(t kg (c) find the amount of salt in the tank after 2 hours. amount (kg (d) find the concentration of salt in the solution in the tank as time approaches infinity. (assume your tank is large enough to hold all the solution.) (kg/l) concentration