My answer for this question is $4.20 (Each pen costs $4.20.).
"Jack bought 6 times more erasers than pens."
Means that there are 6 units more erasers than pens.
Assuming that the number of pens is 1 unit, this means that erasers will be 6 units more, which means it is 7 units.
Ratio wise should be 1:7 (P:E).
This question is quite straightforward. It's a matter of understanding the question (the language usage).