The correct answer is option C) 77
solution::
there can be two cases
numbers can be
case 1 :: 1, 1, 1, 1, 2, 2, 2
possible 7 digits number by this =\({7!\over 3!4!}=35\)
case 2:: 1, 1, 1, 1, 1, 2, 3
possible 7 digits number by this =\({7!\over 5!}=42\)
Total number of seven digit numbers whose sum is 10 using numbers 1, 2, 3 is 35 + 42 = 77