Answer: The base is 7 km.
Explanation:
To find the base, we should use the formula area = 1/2base * height. We know the area and height so plug in this information. 35 = 1/2base * 10. We want to isolate "base". Divide both sides by 10. 3.5 = 1/2base. Now multiply both sides by 2. 7=base.