Quadratic word problem involving ticket sales

[Teresa 41]

Suppose you are an event coordinator for a large performance theater. One of the hottest new Broadway musicals has started tour, and your city is the first stop on the tour. You need to supply information about projected ticket sales to the box office manager. The box office manager uses this infomation to anticipate staffing needs until the tickets sell out. You provide the manager with a quadratic equation that models the expected number of ticket sales for each day x. (x=1 is the day tickets go on sale)

Tickets=-0.2+12x+11
I thought I had this equation worked out right but I was told it was wrong so I can not go any farther with my application problem
I came up with an answer of 12 days and 83 tickets sold and this is the peak.

I am totally confused because then they want you to determine the last day tickets are sold using the the above equation.

 

[stapel]

The box office manager uses this infomation to anticipate staffing needs until the tickets sell out.

Since you're selling "until the tickets sell out", you have to know how many tickets are available to sell. So how many total tickets are there?

When you reply, please include a clear listing of your work and reasoning so far, showing how you arrived at your proposed solution. Thank you!

Eliz.