the cross - section of a stream is a trapezium in shape . if the stream is 10 m wide at the top and the area of cross - section is 640 sq m , the depth of stream is 80 m and width at the bottom is ?
1 / 2 * 80 ( 10 + b ) = 640 b = 6 m answer : b
divide(subtract(640, multiply(multiply(80, divide(const_1, const_2)), 10)), multiply(80, divide(const_1, const_2)))