The sum of the digits in the unit place of all numbers formed with the help of $3,4,5,6$ taken all at a time, is

The correct option is B $108$
When $3$ is in the unit place, then the number of numbers $=3!=6$

Thus, sum of digits in the unit's place $=3\times 6=18$

Similarly, $4\times 6,5\times 6,6\times 6$

Hence, sum of digits in unit place $=18+24+30+36=108$