A Tank Contains 50 Gallons of Water in Which 2 $A ( t )$

A tank contains 50 gallons of water in which 2 pounds of salt is dissolved. A brine solution containing 1.5 pounds of salt per gallon of water is pumped into the tank at the rate of 4 gallons per minute, and the well-stirred mixture is pumped out at the same rate. Let $A ( t )$ represent the amount of salt in the tank at time t. The correct initial value problem for $A ( t )$ is

A) $\frac { d A } { d t } = 6 - 2 A / 25 , A ( 0 ) = 2$
B) $\frac { d A } { d t } = 6 + 2 A / 25 , A ( 0 ) = 2$
C) $\frac { d A } { d t } = 4 + 2 A / 25 , A ( 0 ) = 2$
D) $\frac { d A } { d t } = 1.5 - 2 A / 25 , A ( 0 ) = 0$
E) $\frac { d A } { d t } = 4 - 2 A / 25 , A ( 0 ) = 0$