Fast Lube does oil changes on vehicles in $15$ minutes or less. The variable cost associated with each oil change is

$ $10$$$10$

$($oil$,$ filter, and $15$ minutes of employee$$ time$).$ The fixed costs of running the shop are

$ $18$ comma $000$$$18,000$

each month$($store manager$$ salary, depreciation on shop and$$ equipment, insurance, and property$$ taxes$).$ The shop has the capacity to perform

$1$ comma $8001,800$

oil changes each month. Determine the$$ formula, then calculate the current total product cost of performing