Need formula and answer explained

White Tiger Electronics produces CD players using an automated assembly line process. The standard cost of CD players is $144 per unit (labor, $27; materials, $66; and overhead, $51). The sales price is $325 per unit. To achieve a 13 percent multifacter-productivity improvement by reducing materials costs only, one needs to reduce the materials cost by percent. (Enter your response as a percent rounded to two decimal places.)