Why the answer of question 38 not E?

Cost per customer = Total cost/number of customers.

But we dont know definitely about number of initial customers or cost for each of the stores. Correct me if i am wrong

Percent increase in Total cost per customer = \frac{TCPC (2012) - TCPC (2011)}{TCPC (2012)}

This is equal to:

\frac{\frac{cost (2012)}{n(2012)} + \frac{cost (2011)}{n(2011)}}{\frac{cost (2011)}{n(2011)}}

\frac{cost (2012) * n(2011)}{n(2012) * cost(2011)} + \frac{cost (2011) * n(2011)}{n(2011) * cost(2011)}

\frac{cost (2012)}{cost(2011)}*\frac{n(2011)}{n(2012)} + 1

I think this makes it clear