the cross - section of a tunnel is a trapezium in shape . if the tunnel is 15 m wide at the top and 5 m wide at the bottom and the area of cross - section is 400 sq m , the depth of tunnel is ?
1 / 2 * d ( 15 + 5 ) = 400 d = 400 answer : c
multiply(divide(400, divide(add(15, 5), const_2)), const_10)