18
Question 
(b) Suppose, if the mass of the meter rule be M.
Given, uniform meter rule, so weight (Mg) will act at 25 cm.
Mg produces anticlockwise moment about point o.
Now, in order to balance the 20g weight is tied at 50cm point and it acts in the clockwise direction.
As we know, the principle of moments states that
Anticlockwise moment = Clockwise moment
The weight of half the meter rule is 105 g.
(c) The balancing point will shift towards the 25 cm mark.