Model with function combination

A partially filled pool has $10{,}000$10, comma, 000 liters of water in it when Finn begins to fill it with a hose on a hot, sunny day. The volume, $V$V, in liters, of water coming out of the hose in $m$m minutes is given by the function $V(m)=20m$V, left parenthesis, m, right parenthesis, equals, 20, m, and the volume, $E$E, in liters, of water evaporating in $m$m minutes is given by the function $E(m)=0.1m$E, left parenthesis, m, right parenthesis, equals, 0, point, 1, m.

Let $P$P be the total volume, in liters, of the water in the pool $m$m minutes since Finn started filling it.

$P(m)=$P, left parenthesis, m, right parenthesis, equals

$P(m)=$P, left parenthesis, m, right parenthesis, equals