Convert Hours to Fractions of Hours

Greetings again,

I am attempting to convert a spreadsheet of times (listed in the format 06:15:39.62, where 06 is the hour, 15 is the minutes, 39 is the seconds, and .62 is in truncated miliseconds) into fractions of hours (so, 6.25 [NOT 6:25!]). I've so far been doing it manually for each value, which is quite tedious (doing basic division of seconds and minutes into hours, to find the fraction) but I'd like a single formula which I can then apply to the whole spreadsheet.

Unfortunately, I am at a total loss as to how to do this. Any help is appreciated.