At 9:00 a.m. Monday morning, Thomas fills a beaker with water and places it in the corner of the classroom. At 1:00 p.m. on Tuesday, Thomas examines the beaker and notices that the water level is 42 milliliters. At 11:00 a.m. on Wednesday, the water level has dropped to 31 milliliters. If the evaporation of the water follows a linear function, at what time will the beaker be empty?