Trying to convert duration to number

Hey All, 

Newbie here... I'm building an app for a non-profit that bills in Units.

1 Unit = 15 minutes

I have figured out how to calculate in minutes/hours as a duration based on Start Time/End Time. Here's my duration calculation:
ToTimeOfDay([End Time])-ToTimeOfDay([Start Time])

It yields: 15 minutes, 1 hour, 45 minutes, etc... as the answers. 
Now I need to translate it into Units. (Ex: 15 minutes = 1 Unit, 1 Hour = 4 Units, etc...). I know the first step is to convert the duration into a true number, but I keep getting errors. (See screen shot).

I've tried so many different ways, I'm getting myself confused what I've tried and haven't tried. Some errors are Formula Syntax and others are some type of Boolean depending on which settings I haves tried, another error I was getting was something like incompatible with duration. 

If someone can get me started on a path, that would be most helpful. 

Cheers, Mary



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Mary Perkins
M3TR1CS Business Solutions
mary.perkins@m3tr1cs.com
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