I can help!
So first you need to add $700 to $1000, which will get you $1,700. (this shows you how much more you need to raise so you don't spend more than you earn!)
Now divide $1,700 by $15 and you will get 113 and 1/3 tickets. You can't sell 1.3 of a ticket, so you will round up. You need 114 tickets to be sold!
Hope this helps and good luck! :)