Mr. Lee needs 45 students to volunteer at the science fair. So far, 21 students have signed up. How many more volunteers does he need?
24
Marco has 75 math problems in his summer homework packet. He has done 36 problems so far. How many problems does he have left?
39
Ella made 29 cupcakes for the class. Then, she made 24 more. How many cupcakes did she make?
53