## Thomas' Calculus 13th Edition

$8.5 ^\circ/sec$
Suppose $f(t)$ is the reading of the thermometer at time $t$. Thus, $f(0)=-19$ and $f(14)=100$ Need to use The Mean Value Theorem which states that $f'(c)=\dfrac{f(b)-f(a)}{b-a}$ and $f'(c)=\dfrac{f(14)-f(0)}{(14-0)}=\dfrac{119}{14}=8.5 ^\circ/sec$