1. **Stating the problem:** We have a trapezoid JKMN with area 136 square kilometers. We want to find the area of triangle JKN formed by points J, K, and N. 2. **Understanding the trapezoid:** The trapezoid has bases JM and KN parallel, and KM is the bottom base with length 20 km. The height (distance between the parallel sides) is 8 km. 3. **Formula for trapezoid area:** $$\text{Area} = \frac{(\text{Base}_1 + \text{Base}_2)}{2} \times \text{Height}$$ 4. **Given:** - Area of trapezoid JKMN = 136 - Height = 8 - Bottom base KM = 20 5. **Find the length of the other base (JM):** $$136 = \frac{(JM + 20)}{2} \times 8$$ 6. **Simplify:** $$136 = 4(JM + 20)$$ $$\frac{136}{4} = JM + 20$$ $$34 = JM + 20$$ 7. **Solve for JM:** $$JM = 34 - 20 = 14$$ 8. **Area of triangle JKN:** Triangle JKN shares the same height 8 km and base KN = JM = 14 km (since JM is parallel and equal to KN). 9. **Formula for triangle area:** $$\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}$$ 10. **Calculate:** $$\text{Area}_{\triangle JKN} = \frac{1}{2} \times 14 \times 8 = 7 \times 8 = 56$$ **Final answer:** The area of triangle JKN is **56 square kilometers**.