MLA Citation

Hello, I have written this quote in my essay:

“It would take you thirty years to guess...their chief, [an] extraordinary intellect for a Cooper Indian… dropped and missed the boat! That is actually what he did” (lin. 71-72, 74-75, 79).

My teacher said to check the format of my citation, am I not supposed to use commas? Or do I shrink it to just be (lin. 71-79)? Help!