To solve for number 24, you know that the teacher can grade 5 exams in 3 minutes. He's grading a total of 30 exams. We multiply 5 x 6 to get 30 and we also multiply 3 x 6 to get 18.
To solve for number 25, you know the Dukes have won 3 out of 5 of their last games. The season has 20 games so we multiply 5 x 4 to get 20 and 3 x 4 to get 12.