the cross - section of a cannel is a trapezium in shape . if the cannel is 12 m wide at the top and 2 m wide at the bottom and the area of cross - section is 4200 sq m , the depth of cannel is ?
"1 / 2 * d ( 12 + 2 ) = 4200 d = 600 answer : b"
divide(divide(divide(4200, divide(add(12, 2), const_2)), 2), const_2)