the cross - section of a cannel is a trapezium in shape . if the cannel is 20 m wide at the top and 12 m wide at the bottom and the area of cross - section is 800 sq m , the depth of cannel is ?
"1 / 2 * d ( 20 + 12 ) = 800 d = 50 answer : b"
divide(divide(divide(800, divide(add(20, 12), const_2)), 12), const_2)