the cross section of a canal is trapezium in shape . the canal is 12 m wide at the top and 8 m wide at the bottom . if the area of the cross section is 840 sq . m , the depth of the canal is :
½ ( 12 + 8 ) d = 840 or d = 84 m answer : b
divide(840, divide(add(12, 8), const_2))