A woman pregnant for the second time states that her contrac…

A woman pregnant for the second time states that her contractions began at 6:00 p.m. the previous evening, occurring every 10 minutes.  The contractions eventually stopped, and she was able to sleep for seven hours. She was awakened at 6:00 a.m. by her contractions, which were occurring every 3 to 5 minutes.  She was admitted to the hospital at 8:00 a.m. and was found to be 4 cm.  At 11:30 a.m., her cervix was 10 cm, and she gave birth at 12:00 p.m.  How long was her first stage of labor?