As the applied magnetic field (B=4T) is directed perpendicular to the plane of the frame, it will make angle
(α = 90o ) with each edge of length, L=1m . Here each edge carries current, I=2A.Hence the force on each edge will be
F =BILsinα =4×2×1×sin90o N=8N
The forces on AC and AD will be inclined at an angle 120o . So their resultant will be
= Sqrt (F2+F2+2.F..F.cos120o )=F =8N
Similarly the resultant of two forces on EC and ED will also be F =8N.
These two resultants will act in the same direction EA as the direction of force F on CD.
So the net force on the frame will be =3F=3×8=24N.