The sentence is correctly punctuated with "reported: a subsequent increase in sales," as it adheres to proper punctuation rules and ensures a smooth flow of information in the context of the sentence.
The correct answer is "reported, a."
The sentence "Participating stores [8] reported: a subsequent increase in sales." is appropriately punctuated. The colon after "reported" indicates that what follows will provide more information or elaboration on what the participating stores reported. The comma after "reported" is necessary to separate the introductory clause from the main clause and maintain clarity in the sentence structure.
The usage of "a subsequent increase in sales" after the colon is grammatically correct, providing a concise and clear continuation of the information presented. The phrase effectively communicates that participating stores reported an increase in sales during the statewide Bookstore Day.