Answer
a) $t=d\div r$
b) $t^2-7t+12$
Work Step by Step
a) Dividing both sides by $r$, the given formula, $d=rt$, is equivalent to
$$\begin{aligned}
\frac{d}{r}&=t
\\
t&=d\div r
.\end{aligned}$$Hence, the given formula, in terms of $t$, is $t=d\div r$.
b) Given that $d=t^3-6t^2+5t+12$ and $r=t+1$, then
$$
time=(t^3-6t^2+5t+12)\div(t+1)
.$$By the long division method shown below, then
$$
time=t^2-7t+12
.$$Hence, an expression for the time is $t^2-7t+12$.
