$t=0W(t)as$ a function $of$ time and deter$-$

mine the time when that amount reaches $200$ gallons. $In$ order

$todo$ this, either set $up$ a very easy ODE for $W(t)or$ use your

intuition about the problem.

$(b)$ Write down the differential equation that describes the total

amount $of$ pollutants $P(t)in$ the tank and find the initial con$-$

dition $P(0)of$ this quantity $at$ time $t=0.$ Again, think $in$ terms

$of$ rate $in$ minus rate out.

$(c)$ Find the total amount $of$ pollutants $in$ the tank $at$ the time you

determined $in(a)$