16. Network Rail must, on receipt of a request from the undertaker, from time to time provide the undertaker free of charge with written estimates of the costs, charges, expenses and other liabilities for which the undertaker is or will become liable under this Part (including the amount of the relevant costs referred to in paragraph 15) and with such information as may reasonably enable the undertaker to assess the reasonableness of any such estimate or claim made or to be made under this Part (including any claim relating to the relevant costs).