Confidence Interval

I'm hoping to get a check of my work. I have random samples of temperatures from a city for 2 months.

count = 16 (days)
mean = 35
population standard deviation = 4

count = 20
mean = 33
population standard deviation = 5

Question #1 I need to construct a 90% confidence interval for the difference between the two population mean temperatures in December and January.
Answer #1 For this part I came up with a confidence interval of: -.47 to 4.47. My margin of error was 2.4. I've never had a negative value here in previous problems so it has me worried that I did something very wrong.

Question #2 I also need to state that I can conclude with 90% confidence that the mean temperatures in December and January are different.
Answer #2 For this part, I concluded that it would be an upper tail test with the null hypothesis being <=0 and the alternative hypothesis being >0. My test statistic was 1.33 and p-value was .09. With .09 being less than alpha at .1 I rejected the null and concluded that there is a significant difference in temperatures.

I appreciate any suggestions. Thanks.