Replying to DiffEQ Help

Looking for some help on my Calc 4 homework, it's differential equations. Leave it to me to procrastinate until the night before it's due. Anyways, any help is greatly appreciated:

Consider a tank used in certain hydrodynamic experiments. After one experiment the tank contains 200 liters of a dye solution with a concentration of 1 g/liter. To prepare for the next experiment, the tank is to be rinsed with fresh water flowing in at a rate of 2 liters/min, the well-stirred solution flowing out at the same rate. Find the time that will elapse before the concentration of dye in the tank reaches 1% of its original value.

FUCK story problems. I hate them with a passion. Anyway, the answer is 460.5, or 100ln(100). I have no idea how to find it though so if anyone could help thanks a ton!