Use the commutative and associative properties as needed to simplify the expression. (12+a)+14

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?

Asap! i'm not good math and i'm lost.

Arectangle has a width of 5 cm and a length of 10 cm. if the width is increased by 3, how does the perimeter change?