Hello from MrBillDoesMath! 
Answer: (12*7*6)(x)
 
Discussion: 
The other choices are clearly incorrect. 
(7)(12)(6) + x is NOT equal to (12)(7)(6x)
12(7+6x) is NOT equal to (12)(7)(6x)
12 + 7 + 6x is NOT equal to (12)(7)(6x)
So all of the above statements are incorrect and can not be justified by any property of real numbers
 
Regards, MrB