Working out how much it will cost to buy a set amount of buildings.

Okay so i am building an incremental game and have a formula to work out how much it will cost to buy a set amount of buildings.

This formula is as follows:

((BaseCost * (1.07^b - 1.07^a)) / 0.07)

BaseCost = Starting cost of buildings.

a = number of buildings i already own.

b = number of buildings i will own after buying

This formula will give me a cost if i give it a set amount i want to buy.

But i need to work out how many i can buy with a finite amount of money, without giving it a set number.