Answer:
m = 170 g
Explanation:
Meter stick is suspended at 40 cm mark
So here the torque due to additional mass and torque due to weight of the spring must be counter balanced
given that
1) 220 g is suspended at x = 5 cm
2) 120 g is suspended at x = 90 cm
3) mass of the scale is acting at its mid point i.e. x = 50 cm
now with respect to the suspension point the torque must be balanced
so we have
by solving above equation we have
m = 170 g