Answer
$27$.
Work Step by Step
The given numbers are
$54,81$
Prime factorization of each number is
$54=2\cdot 3 \cdot 3\cdot 3 $
$81=3\cdot 3 \cdot 3 \cdot 3$
Common prime factors are
$=3 \cdot 3 \cdot 3 $
Simplify.
$=27$
Hence, the greatest common factor is $27$.
