Answer
See the answer below.
Work Step by Step
Since P and V are constant, $n\propto 1/T$ and the gas is the same so: $m\propto 1/T$
$12\ g/x=273\ K/300\ K$
$x=13.2\ g$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.