You provided lots of figures but there still seems to be something missing. In general, if someone takes a day off, as paid holiday, they should expect to receive the same pay as if they were at work on that day (excluding any overtime they might have worked).
Although you've stated that the employee works 16 hours per week, you haven't said how this is distributed. If your statement that 'everyone does a 5 day week' means that the employee works 3 hours 12 minutes per day, then a day's holiday pay should be equivalent to 3 hours 12 minutes pay. If, however, the employee works different hours on different days, things can start to get get really complicated! Further information, please!
In general, it would be better to think of things on a weekly basis. The employee normally receives �80.80 per week when they're at work. If you continue to pay the employee �80.80 for each week which includes paid holidays, both you and the employee should be able to see that everything is fair.
Chris