The cross-section of a water channel is a trapezium in shape. If the channel is 14 meters wide at the top and 8 meters wide at the bottom and the area of cross-section is 880 square meters, what is the depth of the channel (in meters)?
Select the correct option
A) 50
B) 60
C) 70
D) 80
E) 90

Rationale: "1 / 2 * d * ( 14 + 8 ) = 880 d = 80 the answer is d ."
Answer: D