J is right, except I would add that you will probably be happier if you eat and drink more on your 100 mile day than you did on your 70 mile day. That means eating and drinking more EARLY in the ride, as opposed to during the last 20-30 miles.
I just rode my first century this year last weekend. I KNOW I need to eat & drink, and I still ate less than I meant to. I finished fine, but I was deeper into my energy reserves than I meant to be. Maybe it was the 40-50 degree weather and extra 3000' of climbing that threw me off. If I had ridden an additional 20 miles like I had thought of doing, I might have come up short. I ate 2 PB&J sandwiches, 4 bottles of energy drink, a package of Donettes, and a chicken teriyaki stick.
We're all different. For me, I'm thinking I should take in at least 200-300 calories every 60-90 minutes (on average) to keep from depleting my energy stores too quickly, based on a solo flat riding speed of 18+ mph.
I burn more than 200-300 calories per 60-90 minutes, but the replacement rate is enough to keep me from completely depleting my reserves over that 100 mile distance. Slower riding would require fewer calories per unit time, but maybe the calories per unit distance might be comparable to the lower calorie range. (That's just a bare-faced guess-stimate.) I drink enough water that I need to make a couple relief stops along the way. All of this works best with snacking along the way rather than a 4-course lunch mid-way through.
For longer rides (150+ miles), I think my energy intake should be at least 300 calories/hour (average), and likely more, because my starting reserve will need to last longer.
Finally, start eating and drinking in the first hour, and keep it up throughout the ride. Finishing with extra energy is lots better than riding 10 miles through a bonk.