As we know, centre of mass is given by, rcom=∑mi∑miri
rcom=m+3mm(ı^+2ȷ^+k^)+3m(−3ı^−2ȷ^+k^)
rcom=4m−8mı^−4mȷ^+4mk^=−2ı^−ȷ^+k^
The magnitude of the position vector of the centre of mass is 22+11+12=6.
It is similar to the magnitude of the option A.