Answer
$5.897$ $°C/hr$
Work Step by Step
The time interval from 8:36 AM to 9:34 AM has length 58 minutes
The change in temperature over this time interval is
$ΔT$ = $-42-(-47.7)$ = $5.7$ °C
$\frac{ΔT}{Δt}$ = $\frac{5.7}{58}$ = $0.0983$ °C/min
$\frac{ΔT}{Δt}$ = $0.0983\times60$ = $5.897$ °C/hr