A substance of mass m kg requires a power input of ‘P’ watt to remain in the molten state at its melting point. When the power is turned off, the sample completely solidifies in time ‘t’ sec. The latent heat of fusion of the  substance is

• A

  $\frac{\mathrm{pm}}{\mathrm{t}}$

• B

  $\frac{\mathrm{pt}}{\mathrm{m}}$

• C

  $\frac{\mathrm{m}}{\mathrm{pt}}$

• D

  $\frac{\mathrm{p} \mathrm{x} {\mathrm{t}}^2}{\mathrm{m}}$