To cite a source in-text, use superscript numerals that correspond to the item in the list of works cited. If you're citing more than one source, don't put a space between the comma and the next reference. The examples below show how this works in the context of different kinds of punctuation:
As previous studies indicate,15,19
Previous studies have validated this speculation.4,7
Previous studies show this to be the case16-18; however...