Let's call the cost of a single pen X.
So you got 4*X + 6*X + 6 = 28
Solving that for X, you get X = 2,2
So the cost of a single pen is 2,2 dollar and the cost for a ten pack is 3,2dollar.
A ten pack of pens at the drug store costs $1 more than two times the cost of a single pen. If you buy 4 single pens and 6 ten packs of pens, the total bill is $28. Find the approximate cost of a single pen?