What exactly is pre-algebra?
Pre-algebra is a name for a course whose objective is to prepare the student for the study of algebra.
What are some of the topics that were considered important to the elementary curriculum?
Whole numbers, measurement units, fractions, equations and formulas, and many others
What does changing the subject of a formula mean?
Changing the subject of a formula means to rearrange the formula so that a different variable is isolated and or focused on.