Find the HCF of $135$, $171$, $192$.

To find the Highest Common Factor (HCF) of $135$, $171$, and $192$, we first perform prime factorization:
* $135=3\times 3\times 3\times 5=3^3\times 5$
* $171=3\times 3\times 19=3^2\times 19$
* $192=2\times 2\times 2\times 2\times 2\times 2\times 3=2^6\times 3$

The common prime factor in all three numbers is $3$.
The lowest power of $3$ present in all factorizations is $3^1=3$.

Thus, $\text{HCF}(135,171,192)=3$.