Option D,
Step-by-step explanation:
Step 1:  Determine the correct expression
So we know for sure that we will be doing 12 - 6 because we have the part where it says the difference of 12 and 6.  That leaves us with Options A and D.  Looking back at the statement we can see that the quotient of 30 and the rest which means that 30 would be the numerator and located at the top.  This gives us option D.
Answer: Option D,