InfoPath Dev

How would I multiply for example, 27:10 hours by 1.5 to get an overtime rate in hours?

I would have a sub selection for the first and last part of the number so something like substring before : to get the first number, then multiply that by 1.5 store to a variable. substring after : then devide by 60 and multiply by 1.5 store this to a second variable. Then add the two variables together and store to a results value.

see attached form.