The magnitudes of \( x \) and \( y \) components of \( \vec{P} \) are \( 5 \) and \( 3 \) respectively. The magnitudes of \( x \) and \( y \) components of \( \vec{P}-\vec{Q} \) are \( 9 \) and \( 7 \), respectively. Then the magnitude of \( \vec{Q} \) is: