Answer
1.4 Hz.
Work Step by Step
Find the spring constant by dividing the magnitude of applied force by the displacement.
$$k=\frac{F}{x}=\frac{mg}{x}=\frac{(66kg)(9.80m/s^2)}{0.005 m}=1.2936 \times 10^5 N/m$$
Find the oscillation frequency from k and the total mass.
$$f=\frac{1}{2 \pi}\sqrt{\frac{k}{m}}=\frac{1}{2 \pi}\sqrt{\frac{1.2936 \times 10^5 N/m }{1766kg}}\approx 1.4Hz$$
