The temperature on a certain morning is -11℃ at 5 a. m. If the temperature drops 3 degree at 6 a.m. and rises 5 degree at 8 a.m. and again drops 3 degree at 9 a.m. What is the temperature at 9 a.m.?

Temperature at 5 a.m. = -11℃
Temperature decreased at 6 a.m. = 3℃ = -3
Temperature raised at 8 a.m. = 5℃ = +5
Temperature decreased at 9 a.m. = 3℃ = -3
Final temperature at 9 a.m. = (-11) + (-3) + (+5) + (-3)
= -11 - 3 + 5 - 3
= -17 + 5
= -12℃.