Setting up initial value problem

[fishys182]

milk containing 6% fat per gallon is pumped into a tank that initially contains 300 gal of milk at 3% fat. the rate at which the milk is pumped in is 3 gal per min, whereas the mixed liquid is pumped out at the same rate.

a) find the number of gallons of fat in the tank at any time.

b) what is the percentage of fat in the tank as time goes to infinity?

this is what i have so far:

r1=3 gal/min
c1 = ... I am not sure about the percents... how to work with them in this kind of problem
r2 = 3 gal/min
c2= yet more confusion
initial volume = V(0) = 300 gal
initial amount = A(0)= 3% ?

 

[courtrigrad]

the weight of 1 gallon of milk is about 8.6 lbs. So use this fact to get the amount of fat per gallons in terms of pounds/gallon. A(0) \doteq 77.4