Hi!
The first thing I would do is see how much the charity has to make to exceed its goal. To do that, I would subtract how much they've already made from their goal.
1200 - 750 = 450
Now, since each ad provides 25 dollars, and the charity wants to exceed its goal, add 25 to 450, to get 475. (What they have to make to exceed their goal)
Now, just find how many ads must be made, or how many 25 dollars, go into 475, by dividing 475 by 25.
475/25 = 19 ads
Of course, if you get this question wrong and instead its 18 because your teacher stated they weren't supposed to exceed the goal and instead just meet it, you can question their wording of the problem.
Hope this helped!