The expression $3(a - 6)$ can be simplified by distributing the $3$ across the terms inside the parentheses:

$3(a - 6) = 3 \cdot a - 3 \cdot 6$

$= 3a - 18$

So, the simplified form of the expression is $3a - 18$.

Would you like further details or have any questions?

Here are some related questions:

1. How do you factor $3a - 18$ back into its original form?
2. What happens if you distribute a negative number instead of 3?
3. How would you solve $3(a - 6) = 0$ for $a$?
4. How can this expression be used in an equation?
5. What if $a = 6$? What does the expression equal?
6. How would the expression change if it was $3(a + 6)$?
7. Can you expand and simplify $3(a - 6) + 2(a + 3)$?
8. How would you distribute if it was $5(2a - 4)$?

Tip: Always double-check your distribution, especially when dealing with negative signs.