The conversation between human and AI assistant.
[|Human|] Evaluate the expression 3x - 3 when x = 4.
[|AI|] When x = 4, the expression 3x - 3 becomes:

3 * 4 - 3 
= 12 - 3 
= 9

So the expression 3x - 3 equals 9 when x = 4.
[|Human|] 
Evaluate the expression 3x - 3 when x = 4.