[SOLVED] Solve System Problem.

Hi, first of all, sorry for posting in English, but I did not find any posts in the forum that are in English ...
I'm trying to make a program, and at the end of the code, I check which variables are missing to be calculated and solve them through a system ... to do this, I keep the list of unused variables in another variable, but texas Does not accept such action.
In the following image I gave an example of the problem!

Is there any way to resolve this?
Thank you all.
I'm trying to make a program, and at the end of the code, I check which variables are missing to be calculated and solve them through a system ... to do this, I keep the list of unused variables in another variable, but texas Does not accept such action.
In the following image I gave an example of the problem!

Is there any way to resolve this?
Thank you all.