I don't understand how to add the fractions

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?

Compare the cost of the bike trips from the two companies shown.for both the cost in a linear function of the number of days which statements is true

If you have 12 feet of string and you cut it into equal length of 5 inches each how much string will be left