Let x be the cost of the pencil.
If the pen costs 2 times the cost of the pencil, then it costs 2x.
Adding the cost of the pen and pencil we get 2x + x = 3x
Since the total cost is $6 then 3x = $6 therefore x = $6 / 3 = $2
One pen is equal to 2 * x which is 2 * $2 = $4
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