The initial temperature is 15ºF
Each passig hour the temperature drops 2 degrees Celcius
First pass the initial temperature from Fahrenheit to Celcius
[tex]\begin{gathered} ºC\cdot\frac{9}{5}+32=ºF \\ (ºF-32)\cdot\frac{5}{9}=ºC \\ (15-32)\cdot\frac{5}{9}=-9.44ºC \\ \end{gathered}[/tex]
The initial temperature is -9.44ºC and the drop is 2ºC per hour (x represent the number of hours), the time lapse is 9 hours
You can calculate the final temperature as
[tex]\begin{gathered} T=-9.44-2x \\ T=-9.44-2\cdot9 \\ T=-27.44ºC \end{gathered}[/tex]
Next pass the temperature back to Fahrenheit using the first formula:
[tex]\begin{gathered} (ºC\cdot\frac{9}{5})+32=ºF \\ (-27.44\cdot\frac{9}{5})+32=-17.392ºF \end{gathered}[/tex]
The final temperature is -17.392ºF, aprox -17ºF
Correct choice is B.
