Robin spent one hour and 50 minutes cleaning is her room if it was 645 when she finished what time was it when she start?

6:45 - 1 hour = 5:45 5:45 - 50 minutes = 4:55

if it was 6:45 and they spent 1 hour 50 minutes subtract that from 6:45. so 6:45-1 hour 50 then it would be 4:55 when they started