1. **State the problem:** We have an isosceles triangle ABC with vertices B(0,0) and C(20,0) on the x-axis. The triangle's area is 240, and AB = AC. We need to find the y-coordinate of vertex A. 2. **Formula for the area of a triangle:** The area $\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}$. 3. **Identify base and height:** The base BC lies on the x-axis with length $20 - 0 = 20$. The height is the y-coordinate of A since A lies above the x-axis. 4. **Set up the area equation:** $$240 = \frac{1}{2} \times 20 \times y_A$$ 5. **Simplify the equation:** $$240 = 10 \times y_A$$ 6. **Solve for $y_A$:** $$y_A = \frac{240}{10} = 24$$ 7. **Check the isosceles condition:** Since AB = AC, A must lie on the vertical line that is the perpendicular bisector of BC, which is at $x = 10$. This is consistent with the problem setup. **Final answer:** The y-coordinate of A is $24$. Therefore, the correct choice is (D) 24.