The cross-section of a river bank is a trapezium in shape. If the river bank is 12 m wide at the top and 8 m wide at the bottom and the area of cross-section is 500 sq m, the depth of river bank is?	Choose the correct choice from the following answers.
A) 20 m  B) 60 m  C) 40 m  D) 50 m  E) 90 m
1/2 * d (12 + 8) = 500   d = 50   ANSWER:50 m
<result>D</result>
The cross-section of a river bank is a trapezium in shape. If the river bank is 12 m wide at the top and 8 m wide at the bottom and the area of cross-section is 500 sq m, the depth of river bank is?