This is a homework question where I don't quite understand what I am being asked to do:
A tank contains $5000$ L of pure water. Brine that contains $30$ g of salt per litre of water is pumped into the tank at a rate of $25$ L/min. Show that the concentration of salt after t minutes (in grams per litre) is:
$$ C(t)= 30t/200+t $$
I am not sure what I am being asked to do?