Question

both are correct—why the difference in comma usage?If the next two nights are sellouts, the play will be extended.The play's run will be extended if the next two nights are sellouts.

Accepted Answer

adverb claues that start sentences must be set off by a comma, but not ones that end sentences=> this is wrong:  The play's run will be extended, if the next two nights are sellouts.

Front	both are correct—why the difference in comma usage? If the next two nights are sellouts, the play will be extended. The play's run will be extended if the next two nights are sellouts.
Back	adverb claues that start sentences must be set off by a comma, but not ones that end sentences => this is wrong: The play's run will be extended, if the next two nights are sellouts.

Nights Play's Run Sentences Correct—Why Difference Comma Usage