What weight wb will cause the system to be in equilibrium? neglect all friction, and state any other assumptions.?

To attain equilibrium there should be net force on the body, so that the object will not be in motion. so for a body of wb, any weight will do as long as there is no external force that is applied to it. the only force that is acting on it is the weight which is going down, and the normal force which is going up, to counter act the weight. and the net force is zero.