If the value of these constants are known, then you can use mldivide: https://www.mathworks.com/help/matlab/ref/mldivide.html
a = 1;
b = 2;
c = 1.4;
d = 1.2;
e = 2.1;
f = 3.2;
g = 1.1;
c1 = 1;
c2 = 2;
c3 = 3;
A = [a b 0;
c d e;
0 f g];
B = [c1; c2; c3];
sol = A\B;
x = sol(1);
y = sol(2);
z = sol(3);
