Please help this is hard

Write an explicit formula that represents the sequence defined by the following recursive formula:

What expression is equivalent to (2x-1)(x-3)?

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?