This question: $1$ point$($s$)$ pos

The rate at which a machine operator's efficiency, $E($expressed as a percentage$),$ changes with respect to time $t$ is given by $\frac{dE}{dt}=30-8t,$ where $t$ is the number of hours the operator has been at work.

a$)$ Find $E(t),$ given that the operator's efficiency after working $2hr$ is $77\%$; that is$,E(2)=77.$

b$)$ Use the answer in part $($a$)$ to find the operator's efficiency after $3hr$; after $5hr.$

a$)E(t)=$

b$)$ The operator's efficiency after $3$ hours is $\%.$

The operator's efficiency after $5$ hours is $$