A subsoiler operating at 400 mm depth requires 15 kW peak drawbar power at 3 km/h speed. The standard is rigidly fixed vertically on the main frame. The resultant soil resistance acts horizontally at a vertical distance of 450 mm from the main frame. The standard has rectangular cross-section with width to thickness ratio of 4:1, and it fails due to bending. If the allowable bending stress is 90 N/mm², the width of the standard in mm will be