Answer:
The height of trapezoid is 7km.
Step-by-step explanation:
Given that the area of trapezoid formula is A = 1/2×(a+b)×h where a and b represents the length and h is the height. By substituing the values, you are able to find the height :
[tex]area = \frac{1}{2} \times (a + b) \times h[/tex]
Let a = 4km,
Let b = 8km,
Let area = 42km²,
[tex]42 = \frac{1}{2} \times (4 + 8) \times h[/tex]
[tex]42 = \frac{1}{2} \times 12 \times h[/tex]
[tex]42 = 6 \times h[/tex]
[tex]6h = 42[/tex]
[tex]h = 7 \: km[/tex]
