Solve the problem.

An efficiency study of the morning shift at a certain factory indicates that an average worker arriving on the job at $8\mathrm{.}00A.M.$ will have produced Qi $)=-f{t}^{3}6t^{2}18t$ units $t$ hours later. At what rate is the worker's rate of production changing with respect to time at $11$:$00$ A$.$M$.?$

$$ units $\frac{?}{h{r}^2}$