1. **State the problem:** Find the height above the first floor of a shopping mall where a 40-foot-long escalator rises at a 30° angle with the horizontal. 2. **Formula and rules:** In a right triangle, the height (opposite side) can be found using the sine function: $$\sin(\theta) = \frac{\text{opposite}}{\text{hypotenuse}}$$ where $\theta = 30^\circ$ and hypotenuse = 40 ft. 3. **Calculate the height:** $$\sin(30^\circ) = \frac{\text{height}}{40}$$ 4. **Solve for height:** $$\text{height} = 40 \times \sin(30^\circ)$$ 5. **Evaluate $\sin(30^\circ)$:** $$\sin(30^\circ) = \frac{1}{2}$$ 6. **Substitute and simplify:** $$\text{height} = 40 \times \frac{1}{2} = 20$$ 7. **Final answer:** The height above the first floor is **20 feet**.