Problem: the cross - section of a cannel is a trapezium in shape . if the cannel is 15 m wide at the top and 9 m wide at the bottom and the area of cross - section is 636 sq m , the depth of cannel is ?
Rationale: "1 / 2 * d ( 15 + 9 ) = 636 d = 53 answer : a"
annotated_formula: divide(divide(divide(636, divide(add(15, 9), const_2)), 9), const_2)