Answer:
[tex]T_{9hr}=-8 C[/tex]
[tex]T_{12hr}=-6 C[/tex]
[tex]T_{15hr}=-3 C[/tex]
[tex]T_{21hr}=-12 C[/tex]
Step-by-step explanation:
The initial temperature at 9 am:
[tex]T_{9hr}=-8 C[/tex]
At 12 hr is 2 degrees higher:
[tex]T_{12hr}=T_{9hr}+2 C=-6 C[/tex]
At 15 hr is 3 degrees higher than 12hr:
[tex]T_{15hr}=T_{12hr}+3 C=-3 C[/tex]
Finally, at 21 hr, is 9 degrees lower than 15 hr:
[tex]T_{21hr}=T_{15hr}-9 C=-12 C[/tex]