Answer:
The need to sell 20 tickets at $15 each to be able to get their balance to $1000.
Step-by-step explanation:
Amount the 9th grade already had = $700
Amount they need = $1000
Let the number of $15 that will make $700 become $1000 be x, then we have the equation:
700 + 15x = 1000
Solving for x, we have what we are looking for.
Subtract 700 from both sides
15x = 1000 - 700
15x = 300
Divide both sides by 15
x = 300/15
= 20