A triangle with vertices at A(20, -30), B(10,-15), and C(5, -20) has been dilated with a center of dilation at the origin. The image of B, point B', has the coordinates (2, -3). What is the scale factor of the dilation?

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?