The vector position of a 3.90 g particle moving in the xy plane varies in time according to ř, = (3Î + 3j)t + 2t² where t is in seconds and is in centimeters. At the same time, the vector position of a 5.90 g particle varies as r² = 3î – Zît² – 6 t. (a) Determine the vector position (in cm) of the center of mass of the system at t = 2.90 s.