Working capital

The sales each month are 100,000/12. If customers take 2.5 months to pay, then it means that the amount owing at any time (including the reporting date) must be 2.5 time the monthly sales. So 2.5 x 100,000/12.

No. We are assuming that on average the sales are 100,000/12 per month (not that they are exactly that much each month). That is possible, and is all we can assume without more information.