Which is the inverse of the function f(x)=1/3 x+5?

Replace the f(x) with y and proceed to make x the subject:
y=1/3x+5
y-5=1/3x
We need to ÷1/3 on both sides, so ×3 on both sides
3(y-5)=x
3y-15=x
Now swap y with x and replace the isolated x with f(x) so the inverse function is:

Okay so there are 8 employees and 200 calls per hour for all in 8 hours then all you need to do is multiply the 200 calls per hour by the 8 employees
200 divided by 8 is 25 and 25  times 8 is 200 so each employee makes 200 calls in their work day 
i really hope i helped you out in some type of way :)))