The cross-section of a canal is shaped like a trapezium. If the canal is 10 m wide at the top and 6 m wide at the bottom and the area of cross-section is 640 square meters, the depth of cannel is?  Choose the correct answer.
A) 26	B) 28	C) 21	D) 80	E) 23
1/2 * d (10 + 6)   = 640   d = 80   Answer: 80
<result>D</result>
The cross-section of a canal is shaped like a trapezium. If the canal is 10 m wide at the top and 6 m wide at the bottom and the area of cross-section is 640 square meters, the depth of cannel is?