There is only one variable, s, whereas simultaneous equations normally contain two or more.
Take the first two eqns: 21-3s-9=31+5s-4. So -15=8s.
Now the second and third: 31+5s-4=41-2s-14 giving us 7s=0.
The two results are inconsistent for s (s=0 and -15/8) and there can be no solution.