Answer
420
Work Step by Step
Set any digit of the number to be 9.
We are left with 5 more digits whose sum is equal to 4
So We have $x_{1}+x_{2}+x_{3}+x_{4}+x_{5}$ = 4
We have n=5 and r=4
The solution of this is given by $C$(8,4)=70
Because any of the six digits can be 9 we multiply the above solution by 6.
70$\times$6= 420
