(3x − 4)(5x + 2) simplify the binomial expression. can anybody explain how to do this ?

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?

Collin did the work to see if 10 is a solution to the equation r/4=2.4

10x − 5y + 14 = 0 whats the answer pls