A simple harmonic oscillator consists of a mass on a frictionless surface, oscillating with an amplitude of $21\mathrm{.}0$ cm on a spring, which has a spring constant of $4\mathrm{.}85$ x $10^3$ N$/$m$.$ If the maximum acceleration of the mass is $39\mathrm{.}6$ m$/$s$2,$ then the mass attached to the spring is how many kg