Let x be the number of hours the new machine was in operation. Then the old machine was (15-x) hours in operation. Your basic equation is 30*(15-x) + 40x = 545. From the equation, x == 9.5 hours. ANSWER. The new machine was 9.5 hours in operation; the old machine (15-9.5) = 5.5 hours. CHECK. 30*5.5 + 40*9.5 = 545 components. ! Precisely correct !