The ball bearings of a dedicated lathe spindle are subjected to a cyclic load during a manufacturing process in an automated plant. During the cycle a bearing experiences a radial load of 416 N for 25 s at 2800 rev/min, 724 N for 42 s at 2800 rev/min and 115 N at 3700 rev/min for 15 s. Calculate the minimum possible basic dynamic load rating (in kN) for that ball bearing for 31000 hours life with 90% reliability.