1. The problem states: If $x = 10$, what is $x + 5$ equal to? 2. We use the substitution method where we replace $x$ with the given value. 3. Substitute $x = 10$ into the expression $x + 5$: $$x + 5 = 10 + 5$$ 4. Simplify the right side: $$10 + 5 = 15$$ 5. Therefore, when $x = 10$, $x + 5$ equals $15$.