“What now Milly?” Elena shouted (Can you have explanation marks inside speech marks??) Yes you can but, in this instance, you would require a question mark because it is really an exclamatory question.
“Nothing’s happening,” replied Sam
You would not need a capital letter for the word “replied” but you would certainly need the comma before the speech marks.
You would have a full stop before the speech marks if you had rearranged the sentence and said :
Sam replied, “Nothing’s happening.”
Hope this helps to clarify.
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