Question 370137
{{{(matrix(2,1,9,6))*2^3 + (matrix(2,1,9,7))*2^2 + (matrix(2,1,9,8))*2 + 1 = 835}}}
The first term can be explained as follows: Pick any 6 places out of a possible 9. These places will be occupied by b's.  The remaining three places can be filled by a or c (2 choices!), and can be done in {{{2^3 = 8}}} ways, assuming repetition. Same explanation applies for the other terms.