David Davis recently fulfilled his long$-$time dream of opening a gym that offers spinning exercise classes for $$10$ per person. To differentiate his gym and better serve his clients, David provides a towel, a bottle of water, and an after$-$workout protein shake to each person participating in a class, at a cost of $$1\mathrm{.}80$ per person. David employs four part$-$time instructors and pays them each $$1,500$ per month. He also pays himself a monthly salary of $$6,000.$ David$$s other monthly costs are $$2,000$ for rent, $$1,500$ for depreciation on his $34$ bikes, and $$1,525$ in utilities and insurance.