Answer
$q=-0.01p+40$
Work Step by Step
We have data points $(p,q)$
$(2500,15)$ and $(2000,20).$
An equation for the line passing through these points:
$q-q_{1}=\displaystyle \frac{q_{2}-q_{1}}{p_{2}-p_{1}}(p-p_{1})$
$q=\displaystyle \frac{5}{-500}(p-2500)+15$
$q=-0.01p-25+15$
$q=-0.01p+40$