Use inverse operations to isolate the unknown while keeping both sides of the equation equal.
What an equation means
An equation states that two expressions have the same value. A solution is a value of the unknown that makes the statement true.
Example
Example: x + 5 = 12
Subtract 5 from both sides. Apply the same operation to both sides of the equation.
\begin{aligned}x + 5 &= 12 \\ x + 5 - 5 &= 12 - 5 \\ x &= 7\end{aligned}
Do the same thing to both sides
When you change one side of an equation, apply the same operation to the other side so the equality stays true.