Calculating fees based on investment in business?

I am a commercial photographer and I have just invested €36,000 in new digital equipment.

I want to pay for this equipment over three years ( I will probably have to upgrade it then) and I am wondering what I should take into account in terms of return on investment over that period?

The equipment will be paid for with money at 8% and let's assume a 5% rate of inflation.

Assuming that the equipment will be used two days per week during that three year period, how much should I be charging for the use of it on each of those days, based on the above figures?

I hope this makes sense! ;-)

Need any other info, just ask.

Thanks.

D.

Obviously there is a market for renting this equipment. What are the competitors charging ?? Surely this is the best way to work out the prices and to be competitive but profitable. What would the residual value of the equipment be in 3 years time ?