ANS:C - 000100000100

It's so simple if you follow the BCD rule i.e., the no. which is greater than 9 (1001) add 6 (0110) to it for getting a valid one.
so, here
01101000 + 00110110 = 10011110

Here you can see last 4-bit group is invalid so add 6 to it.
10011110
+ 0110
---------------
10100100

Now the first 4 bit group becomes invalid so add 6 to it +0110 ---------------> 100000100.
so the answer (c) is correct.