If they manage to sell [tex]t[/tex] tickets, they will earn [tex]15\cdot t[/tex] dollars. We want this number to be at least 1000, so the inequality would be
[tex]15t>1000[/tex]
In order to solve this for t, you only need to divide both sides by 15:
[tex]15t>1000\iff t>\dfrac{1000}{15} = 66.\overbar{6}[/tex]
So, they need to sell at least 67 tickets to have an income of
[tex]15\cdot 67 = 1005[/tex] dollars
