Convert your numbers to Time:
14. 48 > 14:48
15.21 > 15:21
Notice all I did was to replace the Dot with a Colon
Now Excel knows it's dealing with TIME, not just numbers.
Next you will need to Format your total cell as: [H]:MM:SS
The brackets are required.
You will find the format under Custom
So your data should look like this:
4) 30:09:00 <= Formula =SUM(A1:A2), formatted as [H]:MM:SS