Let \( P(3, 2, 3) \), \( Q(4, 6, 2) \) and \( R(7, 3, 2) \) be the vertices of \( \triangle PQR \). Then, the angle \( \angle QPR \) is:
\( \dfrac{\pi}{3} \)
\( \cos^{-1}\!\left(\dfrac{1}{18}\right) \)
\( \dfrac{\pi}{6} \)
\( \cos^{-1}\!\left(\dfrac{7}{18}\right) \)