Mail Marge Time formats

Hi All.

I have mergefield which contains the total duration of a number of
interactions which is stored as a decimal value

e.g. 21.75

this is 21.75 hours and i need a way to convert this to 21 hours and
45 minutes.

I can convert this to minutes (*60) to get 1305 minutes but still
canno work out how to get this to hours and minutes.

Any help is very gratefully accepted.

Thanks