This sounds like a homework assignment. If it is, show us the code you've written to try to solve the problem and ask a specific question about where you're having difficulty and we may be able to provide some guidance.
If you aren't sure where to start because you're not familiar with how to write MATLAB code, I suggest you start with the MATLAB Onramp tutorial (https://www.mathworks.com/support/learn-with-matlab-tutorials.html) to quickly learn the essentials of MATLAB.
If you aren't sure where to start because you're not familiar with the mathematics you'll need to solve the problem, I recommend asking your professor and/or teaching assistant for help.
If this isn't homework and you need to solve that system of equations, don't write your own solver. Just use the backslash operator \ to solve it.
A=[2.08 -1 0 0;-1 2.08 -1 0;0 -1 2.08 -1;0 0 -1 2.08];
b=[200.0 0.8 0.8 40.8]';
x = A\b;
format longg
check = A*x-b % All elements should be small
