Mathematics for IGCSE & O level - Equations (Section 3 - No. 43)
What does it mean to "make the letter the subject" of a formula?
To solve for that letter's value.
To isolate that letter on one side of the equation.
To substitute a known value for that letter.
To eliminate that letter from the equation.
Explication
Changing the subject means rewriting the formula so the target variable is alone.