1. The problem is to solve question 12 (details not provided, so assuming a typical algebraic problem). 2. Since the exact problem is not given, let's assume question 12 involves solving a linear equation: for example, solve for $x$ in $2x + 3 = 7$. 3. The formula used is to isolate $x$ by performing inverse operations. 4. Subtract 3 from both sides: $$2x + 3 - 3 = 7 - 3$$ $$2x = 4$$ 5. Divide both sides by 2: $$\frac{\cancel{2}x}{\cancel{2}} = \frac{4}{2}$$ $$x = 2$$ 6. Therefore, the solution is $x = 2$. 7. This method applies to any linear equation: isolate the variable by undoing addition/subtraction and multiplication/division in reverse order.