Given that the temperature went from:
[tex]-12°F[/tex]To:
[tex]18°F[/tex]You need to find the temperature change between the given temperatures.
Notice that one of them is less than zero (negative) and the other one is greater than zero (positive).
Therefore, you need to subtract the lowest temperature from the highest, in order to determine how much the temperature changed.
It is important to remember the Sign Rules for Multiplication:
[tex][/tex]