A school is thinking about installing low-flush toilets in all of its bathrooms and air hand-dryers to replace paper towel dispensers. Purchasing new toilets for the entire school will cost $22,000. It will need to employ plumbers to fit the toilets at a cost of $9,500. It is estimated that this will save the school $16,000 in water consumption fees over 3 years. The hand-driers will cost $13,500. The cost of employing electricians to install the hand-dryers will come to $4,400. As the school will no longer have to purchase paper towels, it will save $7,300 per year. It also estimates it will save $1,000 per year in cleaning costs, as the bathrooms will take less time to clean and bins will need to be emptied less frequently. However, the school will incur additional electricity costs of $1,700 per year. Calculate the combined payback period for the installation of low-flush toilets and air hand-driers.