A No. 312 radial-contact ball bearing is loaded uniformly (without shock) as follows: 55 percent of the time, 7 kN and 1800 rpm; 25 percent of the time, 14 kN and 1200 rpm; 20 percent of the time, 18 kN and 800 rpm. Estimate the bearing life for 90 percent reliability. Calculate the cumulative damage contribution for each load.