Centre Of Mass

Four particles of masses m, 2m, 3m and 4m are arranged at the corners of a parallelogram with each side equal to a and one of the angle between two adjacent sides as . The parallelogram lies in the plane with mass m at the origin and 4m on the axis. The centre of mass of the arrangement will be located at

The center of mass of a system of three particles of masses and is taken as the origin of a coordinate system. The position vector of a fourth particle of mass such that the center of mass of the four particle system lies at the point is , where is a constant. The value of is