Answer
$x^{4n}$
Work Step by Step
Using the law $a^{m}\times a^{n}=a^{m+n}$ to obtain:
$x^{n}x^{3n}=x^{n}\times x^{3n}=x^{n+3n}=x^{4n}$
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.