the cross - section of a water channel is a trapezium in shape . if the channel is 12 meters wide at the top and 6 meters wide at the bottom and the area of cross - section is 630 square meters , what is the depth of the channel ( in meters ) ?
"1 / 2 * d * ( 12 + 6 ) = 630 d = 70 the answer is c ."
divide(630, divide(add(12, 6), const_2))