Use commas to offset attributions in direct quotations.

An attribution is the part of the sentence that tells you who said the part in quotation marks.

Mary said, "You spent a long time on this."
"You spent," Mary said, "a long time on this."
"You spent a long time on this," Mary said.

No matter where the attribution goes, it must be offset using commas.

See other quotation rules at these sites:

http://englishplus.com/grammar/00000089.htm

http://grammar.ccc.commnet.edu/grammar/marks/quotation.htm

http://andromeda.rutgers.edu/~jlynch/Writing/p.html#punctuation

https://www.grammarly.com/blog/quotation-marks/

Are you ready for the final exam?