Can't get this problem

[DennisG]

set up a differential equation to represent 2 tons of salt entering a 20 ton tank of water each minute while 2 tons of the mixture are drained each minute

[Tide]

\frac {d}{dt} \frac {S^2 + W^2}{S+W} = \dot S

where W(t) is the amount of water in the tank and S is the amount of salt given by S = S_0 + \dot S \times t with \dot S being the constant rate at which salt is added.

[DennisG]

Are you sure about that tide? I could swear I tried that same thing, but I don't know, maybe I was just being an idiot. Thanks for the help