Question 633145
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
tickets= -0.1x^2+12x+11  = {{{-.1(x-60)^2 + 371}}}   | Completing the Square
Note: the vertex form of a Parabola opening up(a>0) or down(a<0), {{{y=a(x-h)^2 +k}}} 
where(h,k) is the vertex  
 Opens down and vertex is (60,371), the Peak sold on one day is 371 tickets on day 60.  
|Sales increasing up to 60 days and then decreasing
{{{-.1(x-60)^2 + 371 = 0}}} 
     (x-60)^2 = 3710
       x = 60 + sqrt(3710) is the last day tikets will be sold. on the 121st day 
{{{drawing(300,300,   -10, 130, -20, 400,  blue(line(60,400,60,-10))  , grid(1),
circle(60, 371,0.7),
graph( 300, 300, -10, 130, -20, 400,0,-.1x^2+12x+11 ))}}}