50.4-2.8=47.6
47.6/4=11.9
Each CD, before tax, cost $11.90.
As you can see above, I subtracted the sales tax from the total price first. Since each CD cost the same amount and there are 4 CDs in all, you can divide the price of all 4 CDs by 4 to find the price of 1 CD.
Hope this helps!