Several construction workers are laying a foundation. Every day they pour in the same amount of concrete that is in the foundation already. For example, if there are three units of concrete on day one, then the workers will add three more units of concrete the next day making six. The next day, they will add six to make a total of twelve and so on. If it takes 88 days to fill the entire foundation with concrete, how many days does it take to fill one-eighth of the foundation?