1. **State the problem:** Solve for $u$ in the equation $$20 = 2u + 3u$$. 2. **Combine like terms:** Since both terms on the right side contain $u$, add their coefficients: $$2u + 3u = (2 + 3)u = 5u$$ 3. **Rewrite the equation:** $$20 = 5u$$ 4. **Isolate $u$ by dividing both sides by 5:** $$u = \frac{20}{5}$$ 5. **Simplify the fraction:** $$u = 4$$ **Final answer:** $$u = 4$$