Take moments about the pivot at 20 cm. (This ensures that we do not need to consider the contact force at the pivot as it contributes no turning moments.)
anticlockwise moments = F x d
= 2 x 0.15
= 0.30 N m
clockwise moments = W x 0.3
= 0.3W
As the rule is balanced we can apply the principle of moments
Take moments about the pivot at 20 cm. (This ensures that we do not need to consider the contact force at the pivot as it contributes no turning moments.)
anticlockwise moments = F x d
= 2 x 0.15
= 0.30 N m
clockwise moments = W x 0.3
= 0.3W
As the rule is balanced we can apply the principle of moments
clockwise moments = anticlockwise moments
0.3W = 0.3
W= 1.0 N