Solution :
Given :
$m= 0.32 \;J/T$
$B= 0.15 \;T$
$\theta= 180^{\circ}$
For unstable equilibrium . the angle between the magnetic moment and the magnetic field is $180^{\circ}$
the potential energy of the magnet.
$U= -mB \cos \theta^{\circ}$
$\qquad= 0.32 \times 0.15 \times (-1)$
$(\cos 180^{\circ} =-1) $
$\qquad= =4.8 \times 10^{-2}\;J$
Answer : $ 4.8 \times 10^{-2}\;J $