A radio station will announce the winner of a contest when 3,200 callers have phoned the station. At 3:00 p.m. 400 callers were counted. At 4:00 p.m. 650 calls had been recorded. By 5:00 p.m. 950 calls had come into the station, and by 6:00 p.m. 1,300 calls had been counted. If the pattern continues, when will the radio station announce a winner?