The distance between two stars of masses \( 3M_s \) and \( 6M_s \) is \( 9R \). Here \( R \) is the mean distance between the centers of the Earth and the Sun, and \( M_s \) is the mass of the Sun. The two stars orbit around their common center of mass in circular orbits with period \( nT \), where \( T \) is the period of Earth’s revolution around the Sun. The value of \( n \) is \( \_\_\_\_ \).
