Find a number that makes a counter example

Julia is going for a walk through the neighborhood. what unit of measure is most appropriate to describe the distance she walks?

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?

What is the missing step in this proof ?