1. **State the problem:** Solve the equation $20 - x = 10$ for $x$. 2. **Isolate the variable:** To find $x$, subtract 20 from both sides: $$20 - x - 20 = 10 - 20$$ which simplifies to $$-x = -10$$ 3. **Solve for $x$:** Multiply both sides by -1 to make $x$ positive: $$x = 10$$ 4. **Check the solution:** Substitute $x = 10$ back into the original equation: $$20 - 10 = 10$$ which is true. **Final answer:** $x = 10$