My YLF is 2 years old and weighs 80 lbs. on the nose. I give her 2 cups in the morning and 2 cups in the evening. If she's still hungry I'll give her ice cubes to munch on, carrots, or broccoli. That seems to entertain her at least.
I also give her 1 large size milkbone per day.
My other dog was fed unlimited. Meaning, when her bowl was empty I'd fill it. She was a unique dog and managed her own eating/weight. I'd end up filling it every other day or so. With this 2 year old though if you put a 40lbs. bag of food on the floor she might eat it all or at least try to!