How much your next n buildings will cost = ((((1 + p) ^ n) - 1) * c) / p, where p is the building's percentage increase (.07 for oil companies, .08 for banks, etc), n is the number you want to buy, and c is the current cost of the next building.
I just served an absolutely perfect Surfer on Acid, with exactly 1.5 oz of all three drinks in it, and I got a 'good' rating. How exactly are the ratings calculated?