Let:
T1 = Initial temperature
T2 = Final temperature
t1 = Initial time
t2 = Final time
Since the temperature changed by steady amount overnight, we can represent the temperature as a function of the time as a straight line:
![\begin{gathered} T(t)=mt+b \\ \text{where:} \\ m=\text{slope}=\text{rate of change} \\ b=y-\text{intercept} \\ so\colon \\ m=(T2-T1)/(t2-t1)=(-2-10)/(19-7)=(-12)/(12)=-1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/6mnrliljj641j5wl0rjxz5qkeftavi9ft1.png)
The temperature decrease by -1 ° F every hour