The fraction of the pizza that is left is 2/8 of the pizza that Lou originally started off with. To explain this in a bit of a simpler manner here, Lou started of with a whole pizza or 8/8 of a pizza. Considering that this man was greedy and hungry and didn't offer either one of us a slice, he ate most of the pizza, or the 6/8 of the pizza that is digesting in his stomach right now. What is left after you subtract 8/8 from 6/8 (8/8 - 6/8=2/8), you'll be left with 2 pizza slices left.
I hope that this helped and that maybe you won't end up like Lou and eat all the pizza for yourself. :P