Find the missing number in the addition of the following numbers, in base seven
(begin{matrix}
4 & 3 & 2 & 1\
1 & 2 & 3 & 4\
* & * & * & *\
1&2&3&4&1
end{matrix})

A.
3453 
B.
5556 
C.
6016 
D.
13453
Correct Answer: Option A
Explanation
4321(_7) + 1234(_7) = 5555(_7)
Missing number = 12341(_7) – 5555(_7)
= 3453(_7)