the cross - section of a cannel is a trapezium in shape . if the cannel is 9 m wide at the top and 7 m wide at the bottom and the area of cross - section is 560 sq m , the depth of cannel is ?
"1 / 2 * d ( 9 + 7 ) = 560 d = 70 answer : c"
divide(divide(divide(560, divide(add(9, 7), const_2)), 7), const_2)