In B you are mixing vector x, which has old values with variables x.1 to x.3 (literal index) with new values. You have to use one of the two notations throughout.
Keep in mind, that x.1 has absolutely nothing to do with the 3-element vector x! So its the best to use the vector notation throughout in your sheet (x[1 instead of x.1, etc).
Likewise in C - you are searching (and Mathcad modifies) the variables x.1, etc., but you still use the static vector x.
I guess the problem is that you think that x.1 references the first element of vector x as does x[1. But x.1 is a completetly different variable like x1 or x_one. It has nothing to do wit the vector x!