A Pond Initially Contains 70,000 Gallons of Water and an Unknown

Multiple Choice

A pond initially contains 70,000 gallons of water and an unknown amount of pesticide. Water containing 0.07 grams of pesticide per gallon flows into the pond at a rate of 360 gallons per hour. The mixture flows out of the pond at the same rate, so the amount of water in the pond remains constant. Assume the pesticide is uniformly mixed throughout the pond.
Which of these is the differential equation for the amount of pesticide, P(t) , in the pond at any time t?

A)
B)
C)
D)