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

• A
  $557$
• B
  $981$
• C
  $1127$
• D
  $2250$