I fail to code the backwards substitution

I managed to write a code on MATLAB for reducing an augmented matrix using Gauss Elimination, and I got an upper triangle matrix, but I do not know how to code backward substitution. This is how I did the reduction:

function sol = GaussianElimination(A,b)

A = [2 4 1;1 1 2;1 1 -1];

b = [2;2;2];

[m n] = size(A)

[m z] = size(b)

A = [A b];

for i = 2:n

    A(i,:) = A(i,:)-(A(i,1)/A(1,1))*A(1,:)

end

for i = 3:n

    A(i,:) = A(i,:)-(A(i,2)/A(2,2))*A(2,:)

end