Answer
$23100$ Employees
Work Step by Step
From the previous part (a), we have
$N=0.38 \sin (0.776t+5.58) +20.4 $
Plug $t=12$ in order to get the value of $N$.
We have
$N=0.38 \sin (0.776 \times (12)+5.58) +20.4 $
Thus, we have $N \approx 23.1$
This means that we find about $23100$ employees.