Cookie calorie math help?

i made betty crocker chocolate chip cookies today, and there are supposedly 18 possible cookies to get out of it, but i got around 24 (maybe more). Assuming the mix made 18 cookies, the serving size for two cookies is 170 calories, 85 each. Since my mix made 24, how many calories are in one cookie? it has to be lower than 85 because my cookies are prob. smaller