Question 1089043
They are really asking for the x-coordinate (or the axis of symmetry for the quadratic function total sales as function of number of stores visited.
Hulu are told average sales per store, {{{a}}} , is a linear function of {{{x}}} (number of stores visited).
It is {{{a-40=-1(x-30)}}}<--->{{{a=-x+70}}} ,
with a slope of {{{-1}}} , and
going through the point with {{{a=40}}} for {{{x=30}}} .
Total sales is given by
{{{y=a*x}}} or {{{y=(-x+70)x}}}--->{{{y=-x^2+70x}}} .
The vertex is a maximum an happens for {{{x=(-70)/(2(-1))=35}}} .