the cross - section of a cannel is a trapezium in shape . if the cannel is 10 m wide at the top and 6 m wide at the bottom and the area of cross - section is 640 sq m , the depth of cannel is ?
"1 / 2 * d ( 10 + 6 ) = 640 d = 80 answer : d"
divide(divide(divide(640, divide(add(10, 6), const_2)), 6), const_2)