It equals 14,000 is the correct answer
At any time 
(min), the volume of solution in the tank is
If 
is the amount of salt in the tank at any time , then the solution has a concentration of 
.
The net rate of change of the amount of salt in the solution, 
, is the difference between the amount flowing in and the amount getting pumped out:
Dropping the units and simplifying, we get the linear ODE
Multiplying both sides by 
allows us to identify the left side as a derivative of a product:
Integrate and divide both sides by to get
The tanks starts off with 30 lb of salt, so 
and we can solve for 
to get a particular solution of
35+____÷5=7
Get rid of 5 so multiply each side by 5(5 times 7=35).
35+__________=35 the answer is 0
-3x^2+5x+12x-20
Combine like terms
-3x^2+17x-20
That is your answer
