A Large Mixing Tank Initially Contains 100 Gallons of Water $A ( t )$

Multiple Choice

A large mixing tank initially contains 100 gallons of water in which 30 pounds of salt have been dissolved. Another brine solution is pumped into the tank at the rate of 4 gallons per minute, and the resulting mixture is pumped out at the same rate. The concentration of the incoming brine solution is 2 pounds of salt per gallon. If $A ( t )$ represents the amount of salt in the tank at time t, the correct differential equation for A is

A) $\frac { d A } { d t } = 8 - .02 A$
B) $\frac { d A } { d t } = 8 - .04 A$
C) $\frac { d A } { d t } = 4 - .04 A$
D) $\frac { d A } { d t } = 2 - .04 A$
E) $\frac { d A } { d t } = 4 - .08 A$