Calculating doctor cost

i am calculating the costing of consulation for our doctor. For example doctor room rent for a month is 15000 and the doctor works 160 hours per month. She does 66 consultations per month. While calculating the cost price of one consultation, how can i calculate the rent cost? One consultation is 15 mins. Should i divide rent by 160 and calculate the rent cost for 15 mins or should i divide the rent cost by 66 consultations?