The orginal question should be interpreted this way:
a uniform metre rule (or ruler) means a beam of 1 metre in length;
a 4N weight (a separated heavy object) being hanged from one end, exerting a downward force;
the rule is being hanged 0.1m from the end with the 4N weight, exerting an upward force (the tension);
uniform metre rule means the CG (centre of gravity) is 0.5m from either end, and the weight of the rule is producing another downward force;
Let W = weight of the rule, T = the tension to "hang" the rule
taking moment about the end with the "4N weight", then
(0.1)(T) = (0.5)(W)
all upward forces = all downward forces, then
T = W + 4
by solving the simultaneous equations
W = 1
so the weight of the rule is 1 N
Hope my words help.
Cheers.