An electric heater with constant heat supply rate is used to convert a certain amount of liquid ammonia to saturated vapour at high pressure. The heater takes $14$ minutes to bring the liquid at $15^\circ\text{C}$ to the boiling point of $50^\circ\text{C}$ and $92$ minutes to convert the liquid at the boiling point wholly to vapour. If the specific heat capacity of liquid ammonia is $4.9\,\text{kJ/kgK}$, the latent heat of vaporisation of ammonia in kJ/kg is