The answer is 26 more times. Below is how I came to that answer.
Here are the variables you need to pull out to perform the equation:
R = number of times the class is rewarded
3R = number of times the class is rewarded multiplied by 3 marbles each time
24 = the number of marbles the jar already has
100 = at least how many marbles you need for a party
You will want to use this '>' symbol but with the line underneath it so it's a greater than or equal to sign, because the jar has to be greater than or equal to 100 marbles to have a party! I can't show the line in the answer through my keyboard, sorry, but make sure to include the line underneath it.
So,
100 > 3R + 24
100 - 24 > 3R
76 > 3R
76/3 > R
25.33333 > R
You round up the 25 to 26 to make it a whole number.
So, the class has to be rewarded at least 26 more times to have a party!