The sales tax in one state is 6 percent, Write a function rule for finding the total cost for an item with selling price x, then find the selling cost of a cd player with the selling price of $160

f (x) =

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.