As arctic air moved into a region where the temperature was originally 17°C, the temperature began falling at a steady rate of 2°C per hour. What was the temperature after 9 hours?

First you would multiply your hours, 9, by how fast the temperature is dropping, - 2 (because it is dropping, your number would be a negative). 9 x - 2 = - 18.

Next add 17 + - 18 to get - 1. - 1°C is your answer.