When changing the subject of a formula, we rearrange the formula so that we have a different subject.
To do this, remember:
Change side, change operation
In other words, if you move a term from one side of the equals sign to the other, change the operation to do the opposite. (The opposite of an operation is called its inverse).
For example, if the term you want to move is adding then when you move it to the other side it subtracts.
Look at the National 4 changing the subject of the formula section before continuing.