$9.$ A mass on a horizontal spring undergoes simple harmonic motion on a frictionless surface with a period of $3$ seconds. If the system has maximum potential energy in the spring when $\backslash ($ t$=0\backslash ),$ what is the first time when the kinetic energy is $\backslash (2/3\backslash )$ of the total energy of the system?

a$)0\mathrm{.}26$ s

b$)0\mathrm{.}46$ s

c$)0\mathrm{.}66$ s

d$)0\mathrm{.}86$ s