A computer software firm provides a $3530$ office for its five systems analysts and plans to hire three additional analysts. To maintain a $210-$ square$-$foot working space per analyst, the firm's owner$-$manager is considering expansion. The cost of expansion is $$45$ per square foot with annual maintenance costs of $$6$per square foot. The useful life of floor space is $14$ years. By how much should employee productivity increase to justify the additional expenditure? The current salary of the systems analysts is $$24,000.$ Round your answer to three decimal places.