mr sato will give each pair of students 3 magnets. So far Mr sato has given 9 pairs of students their 3 magnets..How many more magnets does Mr Sato need so that each pair of students has exactly 3 magnets.There are 24 students in a science class.

24 students makes 12 pairs.

There are 3 pairs to go.
So, how many magnets is that?