1. **State the problem:** Expand the expression $4(5r + t + u)$. 2. **Formula used:** Use the distributive property of multiplication over addition: $$a(b + c + d) = ab + ac + ad$$ 3. **Apply the distributive property:** Multiply each term inside the parentheses by 4: $$4 \times 5r + 4 \times t + 4 \times u$$ 4. **Simplify each term:** $$20r + 4t + 4u$$ 5. **Final answer:** The expanded form of $4(5r + t + u)$ is $$20r + 4t + 4u$$