An 3-kg mass is attached to a spring hanging from the ceiling and allowed to come to rest. Assume that the spring constant is 20 N/m and the damping constant is 6 N-sec/m. At time t = 0, an external force of 6 sin 3t cos 3t is applied to the system. Determine the amplitude and frequency of the steady-state solution. The amplitude is (Type an integer or a decimal. Round to four decimal places as needed.)