Answer
$\{T_{n}\}=\{67-5.5n\},$
$39.5^{o}F$
Work Step by Step
The temperatures are described as
$\left\{\begin{array}{l}
T_{1}=67\\
T_{n}=T_{n-1}-5.5
\end{array}\right.$,
an arihmetic sequence with common difference $d=-5.5$,
and terms representing temperatures at 1000 ft increments.
The n-th term is $T_{n}=T_{1}+(n-1)d$
$T_{n}=67-5.5(n-1)$
The nth term here represents the temperature at (n-1)1000 ft.
If we want it to represent n(1000) ft, then (the first term is $T_{0})$
and
$T_{n}=67-5.5n$
5000 ft is represented with $T_{5}$
$T_{5}=67-5.5(5)=39.5$
