[fever]

I have one small issue with the math... i have limited experience with economics (but the math doesn't scare me)

1) If I've got this right, you're finding x, the floor over 30, where the cost-per-sf equals the revenue-per-sf. The cost increases by 0.4% per floor, but floors don't compound (much to the dismay of many forumers, i'm sure).

Replace MCthirty * (1 + 0.004)^x = spsf * 0.64 with MCthirty * (1 + 0.004x) = spsf * 0.64

with this change it turns out you don't need to fudge your result at all! x = 70