Find the length of the missing side

How do you multiply a mixed fraction by a regular fraction

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?

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?