1. Problem: Solve the two-step equation $2x + 3 = 15$. 2. Formula and rules: To solve two-step equations, first undo addition or subtraction, then undo multiplication or division. 3. Step 1: Subtract 3 from both sides: $$2x + 3 - \cancel{3} = 15 - \cancel{3}$$ $$2x = 12$$ 4. Step 2: Divide both sides by 2: $$\frac{2x}{\cancel{2}} = \frac{12}{\cancel{2}}$$ $$x = 6$$ 5. Explanation: We first isolate the term with $x$ by removing the constant 3. Then, we divide by the coefficient 2 to solve for $x$. 6. Final answer: $x = 6$