The smallest number that is divisible by both 3 and 6 is.

Multiples of a number are always divisible by that number itself.

Few multiples of $3$ are:
$3\times 1=3$
$3\times 2=6$
$3\times 3=9$

Few multiples of $6$ are:
$6\times 1=6$
$6\times 2=12$
$6\times 3=18$

$\therefore$ The smallest multiple that is divisible by both $3$ and $6$ is $6.$

This is the LCM of $3$ and $6.$