The total energy of the harmonic oscillator is given by the formula
E=21kA2...(1)
where, k is the force constant and A is the amplitude.
The potential energy of the oscillator at the given displacement can be written as
U===21k(3A)22×9kA29E
Hence, its kinetic energy is given by
KE==E−9E98E
Thus, the required ratio is
KEE==98EE89
Hence, x=9.