Locate the center of mass of the system shown in FFig. 6.39 (a) if all of the masses are equal; (b) if $m_{2}=m_{4}=2 m_{1}=2 m_{3} ;(\mathrm{c})$ if $m_{1}=1.0 \mathrm{~kg}, m_{2}=2.0 \mathrm{~kg}$
$m_{3}=3.0 \mathrm{~kg},$ and $m_{4}=4.0 \mathrm{~kg} .$