Question 257229
So it appears you were given this or somehow you cam up with this
{{{- .2x^2+12x+11}}}
Either way I assume this is correct.
We apply the quadratic as
{{{x = (-12 +- sqrt( 144-4*(-.2)*(11) ))/(-.4) }}}
and then
{{{x = (-12 +- sqrt( 152.8 ))/(-.4) }}}
which is
{{{x = 60.90307}}}
or
{{{x = -.90307}}}
The average of these 2 is 30.
 The vertex formula is
{{{y = -.2(x-30)^2 + 198}}}
at 30 days, you sell 198 tickets.