Who can help me? about linguistics?

Add the second syllable (again) to the second syllable of singular noun= plural noun...I can't remember if it is supposed to be worded like this or if it is supposed to be written as second syllable (of singular verb) + singular verb = plural verb. I found this question in my Linguistics textbook too: An Introduction to Linguistics by Fromkin, Rodman and Hyams. This cl is pretty hard and wording the morphological rules were confusing sometimes lol.