Answer
$S(q)=0.5q+10$
Work Step by Step
A linear function will have the form
$S(q)=p=mq+b$
The graph contains points
( number of pills, supply price).
Using the points (60, 40) and (100, 60), we find the slope:
$m=\displaystyle \frac{60-40}{100-60}=\frac{20}{40}=0.5$.
The point=slope form:
$p-40=0.5(q-60)$
$p-40=0.5q-30\qquad/+40$
$p=0.5q+10$
or
$S(q)=0.5q+10$
