diagram is missing, but i will try to explain your doubt.
amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.
force is mass*acceleration.
we have a very small mass: 11.4*0.001 kg
if we want 0.035n of force, we need an acceleration:
0.035 = 11.4*0.001*a
a = 0.035/(11.4*0.001) m/s^2
t = 1/400 h ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m
any of the answers are correct.