When is a body said to be in mechanical equilibrium?

Two masses $m$ and $M$ are attached to the strings as shown in the figure. If the system is in equilibrium,then

See the figure given below. $A$ mass of $6 \; kg$ is suspended by a rope of length $2 \; m$ from the ceiling. $A$ force of $50 \; N$ in the horizontal direction is applied at the midpoint $P$ of the rope,as shown. What is the angle the rope makes with the vertical in equilibrium (in $^{\circ}$)? (Take $g = 10 \; m s^{-2}$). Neglect the mass of the rope.

When is an object said to be in equilibrium?

If a body is in equilibrium under a set of non-collinear forces,then the minimum number of forces has to be

$A$ box of mass $m$ is in equilibrium under the application of three forces as shown below. If the magnitude of $F_1$ is $10 \ N$, what is the magnitude of $F_3$ (in $N$)?