1. **Problem statement:** Find $\tan(\alpha)$ in a right triangle where the side opposite $\alpha$ is 21, the side adjacent to $\alpha$ is 20, and the hypotenuse is 29. 2. **Formula:** The tangent of an angle in a right triangle is the ratio of the length of the opposite side to the length of the adjacent side: $$\tan(\alpha) = \frac{\text{opposite}}{\text{adjacent}}$$ 3. **Apply values:** Here, opposite side = 21 and adjacent side = 20, so $$\tan(\alpha) = \frac{21}{20}$$ 4. **Explanation:** Tangent relates the angle to the ratio of the two legs of the triangle, not involving the hypotenuse. 5. **Answer:** The correct choice is B: $\frac{21}{20}$.