Initial temperature: 56 °F
If the temperature drops by 3 °F per hour for 6 hours, then it drops 3*6 = 18 °F. Therefore, after 6 hours the temperature is: 56 °F - 18 °F = 38 °F
If next, the temperature goes up 12 °F in one hour, then after 7 hours the temperature is: 38 °F + 12 °F = 50 °F