1. **Problem statement:** Express the function $x \mapsto x + 10$ in terms of the given functions $h$ and/or $k$. 2. **Given functions:** - $h(x) = x + 5$ for $x \in \mathbb{R}, x > 0$ - $k(x) = \sqrt{x}$ for $x \in \mathbb{R}, x > 0$ 3. **Goal:** Write $f(x) = x + 10$ using $h$ and/or $k$. 4. **Step:** Notice that $h(x) = x + 5$, so if we apply $h$ to $x + 5$, we get: $$h(x + 5) = (x + 5) + 5 = x + 10$$ 5. **Expressing $x + 5$ in terms of $h$:** Since $h(x) = x + 5$, then $x = h(x) - 5$. 6. **Substitute $x + 5$ as $h(x)$:** $$h(x + 5) = h(h(x))$$ because $h(x) = x + 5$, so $x + 5 = h(x)$. 7. **Therefore:** $$f(x) = x + 10 = h(h(x))$$ **Final answer:** $$x \mapsto h(h(x))$$ This means applying $h$ twice to $x$ gives $x + 10$.