Could someone please explain how to do this problem with steps please. No Trolls, No Links please

Write a story that matches with the expression 42x-5 pls hurry

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?

Which of the following contains a variable?