The candidate's solution is correct. They have provided the adjacency matrix and have correctly found the number of 3 step walks and the generating function for walks from points 1-3.
The candidate's solution is complete and solves the problem. The candidate's approach is to first find the adjacency matrix A, then the matrix giving the number of 3 step walks, then the generating function for walks from point i → j, and finally the generating function for walks from points 1 → 3.