One-step equations and expressions
Undo the operation attached to the variable by doing the opposite to both sides of the equation.
A worked example
Solve x + 24 = 40 by subtracting 24 from both sides, which leaves x = 16.
The mistake people actually make
"4 less than n" is written n − 4, not 4 − n. Subtraction order matters even though addition order does not.