An internal combustion engine has a rotating unbalance of 1.0 kg-m and operates between 800 and 2000 rpm. When attached directly to the floor, it transmitted a force of 7,018 N at 800 rpm and 43,865 N at 1800 rpm. Assume the damping ratio of the isolator is 0.08 and the mass of the engine is 200 kg. Find the stiffness of the isolator that is necessary to reduce the force transmitted to the floor to 6,000 N over the operating-speed range of the engine.