Let

be the number pf Pre-Algebra students,a dn

be the number of Beginning Algebra students.

From the statement "Mr. Alfaro has 3 times as many Pre-Algebra students than Beginning Algebra students" we may write:

You see this is a bit different from the previous problems because we are give that one quantity is a certain multiple of the other rather than being told one is a certain amount more or less than the other.

From the statement "Mr. Alfaro has a total of 72 students" we may write:

Now, what should you do next?