Two blocks of masses \( 10 \, \text{kg} \) and \( 30 \, \text{kg} \) are placed on the same straight line with coordinates \( (0, 0) \, \text{cm} \) and \( (x, 0) \, \text{cm} \) respectively. The block of \( 10 \, \text{kg} \) is moved on the same line through a distance of \( 6 \, \text{cm} \) towards the other block. The distance through which the block of \( 30 \, \text{kg} \) must be moved to keep the position of centre of mass of the system unchanged is:
