When is a body said to be in mechanical equilibrium?

If the tension in the horizontal wire shown in the figure is $30 \text{ N}$,then the weight $W$ and tension in the wire $OA$ are respectively:

$A$ weight $Mg$ is suspended from the middle of a rope whose ends are at the same level. The rope is no longer horizontal. The minimum tension required to completely straighten the rope is ......

Which of the following sets of concurrent forces may be in equilibrium?

$A$ mass of $10\,kg$ is suspended vertically by a rope from the roof. When a horizontal force is applied on the rope at some point,the rope deviates at an angle of $45^o$ from the vertical. If the suspended mass is at equilibrium,the magnitude of the force applied is .......... $N$ $(g = 10\,ms^{-2})$.

Find the magnitude of the unknown forces $x$ and $y$ if the sum of all forces is zero.