Hi, I am having trouble solving this problem:

A 1000 gallon holding tank that catches runoff from some chemical process

initially has 800 gallons of water with 2 ounces of pollution dissolved in it.

Polluted water flows into the tank at a rate of 3 gal/hr and contains 5 ounces/gal of

pollution in it. A well mixed solution leaves the tank at 3 gal/hr as well. When the

amount of pollution reaches 500 ounces the inflow of polluted water is cut off and

fresh water will enter the tank at a decreased rate of 2 gallons while the outflow is

increased to 4 gal.hr. Determine the amount of pollution in the tank at any time t.

This site has the answer but does not really give any details. It is the 2nd example.

Pauls Online Notes : Differential Equations - Modeling with First Order DE's
Thank you very much for your time in helping me.