From the expression in the end, we can distribute the multiplication by 3 to get:

The order of the addtion doesn't change the result, so these three expression are the same for every value of x:

But the other two, 3x + 4 and x + 12, are not the same, so we can check if they will give the same result.
The result for 3(x + 4) is and x = 2 is:

And the results for 3x + 4 and x + 12 when x = 2 are:

Which are not the same as 18.
Thus, the expressions that would give different answer are 3x + 4 and x + 12.