sales tax = 6% or 6/100.
assuming tax is added onto the item:
total cost function f(x) = price + tax
however, assuming the cost price = sales price - tax, then:
f(x) = sales price - tax
This is not really a business or accounting forum, its a maths forum, so you need to be clearer about business or accounting terms such as total cost, selling price, selling cost.
