the cross - section of a cannel is a trapezium in shape . if the cannel is 11 m wide at the top and 9 m wide at the bottom and the area of cross - section is 960 sq m , the depth of cannel is ?
"1 / 2 * d ( 11 + 9 ) = 960 d = 96 answer : e"
divide(divide(divide(960, divide(add(11, 9), const_2)), 9), const_2)