We start on the ones place 6 + 1 + 2 = 9, the sum of the digits in the ones place is not up to 10, we will not regroup this ones place.
So, basically the answer to 13a is NO. Since we are not able to regroup the ones place there is no regrouped tens to add, therefore the answer to 13b is also NO.
Next is the tens place, 4 +2 +5 = 11, the sum of the digits in the ones place is up to 10 so we regroup the tens place.
Thus, the answer to 13c is YES.
Since, we regrouped the ones place, we add the regrouped hundred, thus the answer to 13d is YES.
