So we have the equation:

Where x represents the hours passed after 5 am and y represents the temperature in degrees Fahrenheit. We are being asked about the temperature at 9 am so we need to express 9 am in terms of hours passed after 5 am. Since there's a difference of 4 hours between this two times then we must use x=4 and the result of substituting x by 4 in the former equation will give us the temperature we are looking for:

So the temperature in october at 9 am is 70.98°F so the best approximation would be option C, 71°F.