1. Stating the problem: Solve the equation $x + 15 = 30$ for $x$. 2. Formula and rules: To isolate $x$, subtract 15 from both sides of the equation. 3. Intermediate work: $$x + 15 = 30$$ Subtract 15 from both sides: $$x + \cancel{15} - \cancel{15} = 30 - 15$$ Simplify: $$x = 15$$ 4. Explanation: We moved 15 to the right side by subtracting it from both sides, leaving $x$ alone on the left. Final answer: $x = 15$