Answer
$9$
Work Step by Step
Factor each number completely to obtain:
$27 = 3 \cdot 3 \cdot 3
\\54 = 2 \cdot 3 \cdot 3 \cdot 3
\\63= 3 \cdot 3 \cdot 7$
Since two 3s are common to both, the greatest common factor of the two given numbers is:
$3 \cdot 3 = 9$
