Answer:
12.3 divided by 0.4 is 30.75
Explanation:
You then go to letter A and 123/4 is also 30.75
but you go through the rest of the choices just in case. 
B is 3.075 so that is incorrect 
C is 307.5 so that is also incorrect 
D is 3075 and that is incorrect and not 30.75.
Therefore your answer is A. 
30.75 = 30.75.
Hope this helps :)