Use the cosine rule in a non-right-angled triangle

Consider the non-right-angled triangle \(STU\)

Side \(s\) is opposite angle \(S\) and is unknown. Side \(t\) is opposite angle \(T\) and is 7 m. Side \(u\) is opposite angle \(U\) and is 7 m

Sides \(t\) and \(u\) meet at vertex \(S\). The included angle between them is \(S=68^{\circ}\). Find side \(s\)