Community Tip - Did you get an answer that solved your problem? Please mark it as an Accepted Solution so others with the same problem can find the answer easily. X
Solving directly as Alan had shown sure is the better way, I guess.
If you still want to use the solve block, the guess for X has to be a 4x4 matrix.
The symbolic solution is very cumbersome and unhandy. Mathcads symbolics still has big problems with vector and matrix equations and often will solve for single elements only.