Adding a new lathe machine into the manufacturing process, a company reduced processing time for each unit so that output is increased by $25\%$ with less material but needed to add one skilled worker to operate the machine. Under the old process, five workers could produce $60$ units per hour. Labor costs are $$12/$hour and material input were previously $$16/$unit$.$ For the new process, the material now is $$10/$unit$.$ Overhead is charged at $1\mathrm{.}6$ times the direct labor cost. Finished units sell for $$31$ each. What will be the productivity growth be if the number of workers remains the same, $5$ workers, in both old and new situations $($material cost remains unchanged as per the original statement?