Answer
Net force = 0
So, $m_{1}g+m_{2}g+m_{3}g=N$
$N=1.96N$
Balancing net torque = $m_{1}g\times100+m_{2}g\times80+m_{3}g\times15-50N=98-98=0$
Hence, net torque about x = 100 cm is zero.
Hence, proved.
Work Step by Step
Net force = 0
So, $m_{1}g+m_{2}g+m_{3}g=N$
$N=1.96N$
Balancing net torque = $m_{1}g\times100+m_{2}g\times80+m_{3}g\times15-50N=98-98=0$
Hence, net torque about x = 100 cm is zero.
Hence, proved.