Hey Erie.
In order to find the price of each DVD, you must find the subtotal not including tax. To do this, subtract the tax from the total, or $85.74-$5.04. The subtotal without tax is $80.70.
Because each of the 6 DVDs are the same price, divide this subtotal without tax by 6. This should give you $13.45, the price of each DVD.
The equation for this is 6x+5.04 = 85.74, where x is the price of each DVD.