Tank A contains 80 gallons of water in which 20 pounds of salt has been dissolved. Tank B contains 30 gallons of water in which 5 pounds of salt has been dissolved. A brine mixture with a concentration of 0.5 pounds of salt per gallon of water is pumped into Tank A at the rate of 4 gallons per minute. The well-mixed solution is then pumped from tank A to tank B at the rate of 6 gallons per minute. The solution from tank B is also pumped through another pipe into tank A at the rate of 2 gallons per minute, and the solution from tank B is also pumped out the of the system at the rate of 4 gallons per minute. The correct differential equations with initials conditions for the amounts, x(t) and y(t), of salt in tanks A and B, respectively, at time t are :a. dx/dt=2-x/40+y/5,dy/dt=x/40-y/3,x(0 )=20,y(0)=5b. dx/dt=2-3x/40+y/15,dy/dt=3x/40-y/5, x(0)=20,y(0)=5c. dx/dt=4-3x/40+y/15,dy/dt=3x/40-y/5, x(0)=20,y(0)=5d. dx/dt=4-x/40+y/5,dy/dt=x/40-y/3,x(0 )=20,y(0)=5