On average, donna's cafe has 18 customers, which represents 36% of the total approved occupancy by the fire department.

I am not sure if I understand what you are asking completely, but if you are trying to find how many the maximum customers you can have approved by the fire department, you divide 36% by 18, which gives you 2% per person. To get the maximum allowed number of people, you divide 100% by 2%, which gives you 50 people.

50 is the total occupancy of the fire department.