Question 367056
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Hi, 
Tickets= -0.4x^2+20x+122.1 
a) downward, coefficient of the squared term is negative
b) substitute values of 10,20,40,50 for x to obatain number of tickets
c){{{x = (-20 +- sqrt( 595.36))/(.8)=(-20 +- 24.4)/(-.8)}}}
x = -5.5 and x = 55.55 the last day tickets will be sold
d)  55.55 - 60.05/2  = 25.525
e. calculate value of x = 25.525 for the number of tickets
f) answers to d and e are the vertex points
will let you finish up
{{{graph( 300, 300,-500,500,-500,500,-.4x^2+20x + 122.1) }}}