1. **Problem statement:** We have a right triangle with a hypotenuse of length 12 and one angle of 30°. We need to find the length of side $a$, which is opposite the 30° angle. 2. **Relevant formula:** In a right triangle, the side opposite an angle $\theta$ is related to the hypotenuse $c$ by the sine function: $$a = c \times \sin(\theta)$$ 3. **Apply the formula:** Here, $c = 12$ and $\theta = 30^\circ$. $$a = 12 \times \sin(30^\circ)$$ 4. **Evaluate $\sin(30^\circ)$:** $$\sin(30^\circ) = \frac{1}{2}$$ 5. **Calculate $a$:** $$a = 12 \times \frac{1}{2} = 6$$ 6. **Answer:** The length of side $a$ is 6. This uses the basic trigonometric relationship in right triangles and the known sine value for 30°.