A point mass m is located at (0,a). Where should the 2m mass be kept, so that centre of mass lies at origin

The centre of mass of a body lies

A point object of mass m is kept at (a, 0) along x-axis. What mass should be kept at (-3a,0), so that centre of mass lies at origin ?

The centre of mass of three particles of masses 1 kg, 2kg and 3 kg lies at the point (3m, 3m, 3m) where should a fourth particles of mass 4 kg be positioned so that centre of mass of the four particle system at (1m, 1m, 1m) ?

The centre of mass of three particles of masses 1kg, 2 kg and 3kg lies at the point (3m, 3m, 3m). Where should a fourth particle of mass 4 kg be positioned so that the centre of mass of the four particle system lies at the point (1m, 1m, 1m)?

The coordinates of the centre of mass of a system of three particles of mass 1g,2g and 3g are (2,2,2). Where should a fourth particle of mass 4 g be positioned so that the centre of mass of the four particle system is at the origin of the three-dimensional coordinate system ?

Centre of mass of three particles of masses 1 kg, 2 kg and 3 kg lies at the point (1,2,3) and centre of mass of another system of particles 3 kg and 3 kg lies at the point (-1, 3, -2) . Where should we put a particle of mass 5 kg so that the centre of mass of entire system lies at the centre of mass of first system ?