Answer
$-2t^2+4t$
Work Step by Step
The number of people who catch cold is, $5t-3t^2+t^3$ and the number of people who recover is, $t-t^2+t^3.$
Thus, the number of people who are still ill with cold is the number of people who catch cold minus the number of people who recover.
$5t-3t^2+t^3-(t-t^2+t^3)$
$=4t-2t^2$
Thus, in standard form, $-2t^2+4t$.
