We have a total of 29 days from which 20 had higher temperature, so we are left with 9 days that could be higher or lower, 50% each possibility, so the total probability for the 29th day to be below 45F is 4.5 divided by 29, 4.5 because we have 50% chance of the 9 left days, so that is:
4.5/29 = 0.155
that is 15.5% that is the total experimental probability that the 29th day the temperature would be below 45F
