(1) Any utility filing a rate increase shall be responsible for preparing prior to filing and for maintaining after filing, work papers sufficient to support the filing. Any request for work papers other than those required in ARM 38.5.121 to 38.5.180, inclusive, shall be answered within 15 working days upon receipt of said request by the utility. In the event that there shall be a delay beyond said period the utility shall notify the commission and present a written explanation therefore. If such written explanation does not set forth good cause for refusal or delay response to the request, the commission shall so notify the utility in writing. If the utility then fails to answer the request promptly, the commission may issue such order as is reasonable under the circumstances. In addition to the working paper support, the following specific material normally prepared by the filing utility, related to the test period and subsequent periods, shall be available for the commission's verification and analysis:

(a) Copies of monthly financial report;

(b) Copies of accounting analyses of balance sheet accounts;

(c) Complete trial balances of all the balance sheet accounts at the beginning and end of the 12 months of actual experience used for the filing;

(d) Analyses of the various miscellaneous revenues;

(e) Analyses of surplus and capital surplus accounts.