A work sampling study on 4 janitors showed that 3,508 of 16,000 (4,000 x 4 janitors) observations in a 2-week period correspond to cleaning window panes. During the said period, the buildings 480 window panes were cleaned twice times. Assume 105% performance rating, and 18% allowance applied as a fraction of the whole workday. Assume 8 hours per day, 5 workdays per week. Find the standard time of cleaning one window pane, in mins