Question 1025198
{{{q(90-q) = 400}}}
==> {{{q(18-q) = 80}}}
<==> {{{q^2 - 18q+80 = 0}}}
==> (q-8)(q-10) = 0
==> q = 8, 10.

==> You must order 8 or 10 of the specialized metallic paints for the average profit to be $400 per quart.