Step 1: Write the expressions for total energy and potential energy in SHM.
For a particle executing SHM,
\[
\text{Total Energy}=\frac{1}{2}kA^2
\]
Potential energy at displacement \(x\) is
\[
U=\frac{1}{2}kx^2
\]
Hence kinetic energy is
\[
K=\frac{1}{2}k(A^2-x^2)
\]
Step 2: Substitute the given values.
Given,
\[
A=10\,\text{cm}
\]
and
\[
x=6\,\text{cm}
\]
Therefore,
\[
K\propto A^2-x^2
\]
\[
=10^2-6^2
\]
\[
=100-36
\]
\[
=64
\]
Also,
\[
U\propto x^2
\]
\[
=6^2
\]
\[
=36
\]
Step 3: Find the ratio \(K:U\).
\[
K:U=64:36
\]
Dividing by \(4\),
\[
K:U=16:9
\]
Step 4: Final conclusion.
Hence, the required ratio is
\[
\boxed{16:9}
\]