Anybody wanna do a zoom or a padlet and just talk. Please i'm very bored right now

Which is an equation for the nth terms of the sequence 12,15,18,21

How do i do this activity, is appreciated

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?