To the extent reasonably feasible, cost overages shall be agreed to in writing by the client before the editorial company proceeds with the work in question. If prior written approval is not feasible, the editorial company shall promptly confirm the overage in writing. The approval of an overage by an agency representative shall constitute an agreement by the agency to pay for the overage at the rate specified in the estimate or at the rate specified at the time the overage is to be incurred, together with mark-up on the overage at the applicable rate, if any, specified in the estimate.