1. **State the problem:** Ken made a wooden door stop shaped like a triangular prism with legs 7 cm and 15 cm, length 4 cm, and weight 155.4 grams. We need to find which wood type Ken used based on the density. 2. **Formula for volume of a triangular prism:** $$V = \text{area of triangular base} \times \text{length}$$ 3. **Calculate the area of the triangular base:** The base is a right triangle with legs 7 cm and 15 cm. $$\text{Area} = \frac{1}{2} \times 7 \times 15 = \frac{1}{2} \times 105 = 52.5 \text{ cm}^2$$ 4. **Calculate the volume of the prism:** $$V = 52.5 \times 4 = 210 \text{ cm}^3$$ 5. **Use the density formula:** $$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$$ Given mass = 155.4 grams, volume = 210 cm³. 6. **Calculate the density of the door stop:** $$\text{Density} = \frac{155.4}{210} = 0.74 \text{ g/cm}^3$$ 7. **Compare with given wood densities:** Maple: 0.68, Pine: 0.48, Spruce: 0.56, Bamboo: 0.34, Oak: 0.74, Balsa: 0.16 8. **Conclusion:** The density matches Oak wood. **Final answer:** Ken used Oak wood to make the door stop.