The temperature at 5:00 a.m. was –6 °F. By 3:00 p.m., the temperature had risen to a high of 36 °F. If the temperature at 8:00 p.m. decreased from the high by of the change in temperature in Fahrenheit degrees from 5:00 a.m. to 3:00 p.m., what was the temperature at 8:00 p.m.?

Let T denote temperature, °F

At 5:00 a.m.:
T = -6 °F

At 3:00 p.m.:
T = 36 °F
The rise in temperature from 5:00 am is
36 - (-6) = 42 °F

At 8:00 p.m.:
The temperature decreased from the high of 36 °F by 42 °F (equal to the amount of increase from 5:00 a.m. to 3:00 p.m.).
Therefore the temperature at 8:00 p.m. is
36 - 42 = -6 °F

Answer: -6 °F