A \(150 \mathrm{~kg}\) engine operates at speeds between 1000 and \(2000 \mathrm{rpm}\). It is desired to achieve at least 85 percent isolation at all speeds. The only readily available isolator has a stiffness of \(5 \times 10^{5} \mathrm{~N} / \mathrm{m}\). How much mass must be added to the engine to achieve the desired isolation?