In this question, we use law of cosine which is
[tex] RS^2 = RT^2 + ST^2 -2(RT)(ST) cos T [/tex]
Substituting the given values of RS,RT, ST , we will get
[tex] 3^2 = 5^2 + 7^2 -2(5)(7) cos T
\\
9 = 25 +49 - 70 cos T [/tex]
[tex] cos T = \frac{65}{70} [/tex]
Taking inverse cosine on both sides
[tex] T = cos^{-1} ( \frac{65}{70}) [/tex]
[tex] T = 22 [/tex]
