500 gallon Tank filled with pure water, brine with 2 lbs of salt/gal pumped in at 5 gal/min, Mixed solution pumped out at same rate of 5 gal/min. Find the number A(t) of pounds of salt in tak at time...

A large tank is filled to capacity with 500 gallons of pure water
Brine containing 2 pounds of salt per gallon is pumped into the tank at the rate of 5gal/min
The well mixed solution is pumped out at the same rate.
To find number of pounds of salt A(t) in the tank at time t.
In 1 min 10 pounds of salt enters the tank .
Since this salt mix up in the 500 gallons hence...