A sample of mass \(0.40 \text{ kg}\) of a pure solid at its melting point \(273 \text{ K}\) is heated in an insulated container by a source that transfers energy to the sample at a constant rate \(P\). The graph shows the temperature \(T\) of the sample as a function of time \(t\). The specific heat capacity of the substance in its liquid phase is \(2000 \text{ J/(kg}\cdot\text{K)}\). Based on the graph, what is the latent heat of fusion \(L_f\) of the substance?