You need to define is the values given stand for the meaure of the angles in degrees or for the lengths of the sides.
It it is fhe former, then you can write:
5s + 20s + s + 24° = 180°
=> 26s + 24° = 180°
=> 26s = 180° - 24°
=> 26s = 156°
=> s = 156° / 26 = 6°
If it is the latter, then you have to use the law of cosines and or the law of sines.
