If you don’t know the tax price/value then you can’t add that on the total amount. So, if we don’t know the value of that we can just forget about it for now.
You do $10.19-$1.25 (to get just the price of the pens) =$8.94
To get the value of one pen just do $8.94 divided by 6 (the total number of pens)=$1.49
$1.49=Price for one pen
Hope this helps :)