The y intercept is 1/2; the slope is -1/4 (0, 1) and (1, 3) or (1, 2) and (2, 4) what would that be?

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?