A brine tank with a capacity of 80 liters initially contains 30 liters of solution containing 10 g of salt. Solution containing 2 g of salt per liter enters the tank through a pipe at a rate of 4 liters/min, while the mixture flows out of the tank through another pipe at a rate of 2 liters/min. (a) Let x(t) be the amount of salt (in grams) in the tank at time t. Write a differential equation satisfied by x(t). (b) Solve for x(t), using the initial condition described in the problem. (c) What is the concentration (in g/L) of salt in the tank at the instant that it overflows