Rule 30 3

Where the answer to an interrogatory may be derived from the books or documents of the party upon whom the interrogatory has been served and the burden of deriving the answer is substantially the same for the party serving the interrogatory as for the party served, it is a sufficient answer to such interrogatory to specify the records, books or documents from which the answer may be derived and to afford to the party serving the interrogatory reasonable opportunity to examine, audit or inspect them and to make copies, compilations or summaries.