Question 746417
Volume of a pyramid = 1/3 x Area of base x height
                    = 1/3 x 900 x 40
                    = 12000 cm^3

Volume of tank = length x breadth x height
               = 40 x 40 x 40
               = 64000 cm^3

    64000 - 12000 = 52000 cm^3 water left

              52000 cm^3 / 40 x 40  = h
                   h = 32.5cm.