The cross-section of a cannel is a trapezium in shape. If the cannel is 10 m wide at the top and 6 m wide at the bottom and the area of cross-section is 640 sq m, the depth of cannel is?
20 m
60 m
40 m
80 m
Explanation:
1/2 $\times$ d (10 + 6) = 640
d = 80