Step 1: Calculate the angular frequency.
For a mass-spring system,
\[
\omega=\sqrt{\frac{k}{m}}.
\]
Given,
\[
k=8\,\text{N m}^{-1}
\]
and
\[
m=2\,\text{kg}.
\]
Therefore,
\[
\omega=\sqrt{\frac{8}{2}}
\]
\[
\omega=\sqrt{4}
\]
\[
\omega=2\,\text{rad s}^{-1}.
\]
Step 2: Calculate the time period.
The time period is
\[
T=\frac{2\pi}{\omega}.
\]
Substituting \(\omega=2\),
\[
T=\frac{2\pi}{2}
\]
\[
T=\pi\ \text{s}.
\]
Using
\[
\pi \approx \frac{22}{7},
\]
\[
T=\frac{22}{7}\ \text{s}.
\]
Step 3: Find the number of oscillations in \(66\,\text{s}\).
Number of cycles,
\[
n=\frac{\text{Total Time}}{\text{Time Period}}
\]
\[
n=\frac{66}{22/7}
\]
\[
n=66\times \frac{7}{22}
\]
\[
n=3\times 7
\]
\[
n=21.
\]
Step 4: Final conclusion.
Hence, the number of cycles completed in \(66\,\text{s}\) is
\[
\boxed{21}
\]