The problem gives this information:

You need to supply information about projected ticket sales to the box office manager. The box office manager uses this information 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 = -0.2x^2 + 12x + 11

use the quadratic equation to determine the last day the tickets will be sold. (Note: write your answer in terms of the number of days after ticket sales begin).

Now, for some reason I can't seem to get started on this problem...would someone give me a kick in the right direction?