Answer:
There are probably more than this but here
$12 for pens would give you 6
$12 for notepads would give you 4
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$18 for notepads would give you 6
$6 for pens would give you 3
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$21 for for notepads would give you 7
$2 or pens would give you 1
and $1 left
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$6 for notepads would give you 2
$18 for pens would give you 9