Trying to help my sister and need help helping her

Anyone know? will mark brainliest if correct!

Mrs. morton has a special reward system for her class. when all her students behave well, she rewards them by putting 3 marbles into a marble jar. when the jar has 100 or more marbles, the students have a party. right now, the the jar has 24 marbles. how could mrs. morton reward the class in order for the students to have a party?

3382-299=3383- ? fill in the blank?