Question

The first recorded tempature is 109F. Four hours later the second tempature is 58F . What is the change in tempature

Answer 1

You can easily solve this question using basic math:
109-59=51. The temperature difference is 51 degrees

Answer 2

Salutations!

First temperature recorded = 109F

Second temperature recorded = 58F

Notice the change is temperature? Is  the temperature increasing or decreasing?

Its decreasing! From 109 it has stepped down to 58F

Therefore, you will be subtracting --- 

$190-58=51$

The answer is 51F.

Hope I helped (:

have a great day!