Heat Is Added to a Pure Substance in a Closed

Heat is added to a pure substance in a closed container at a constant rate. The figure shows a graph of the temperature of the substance as a function of time. If L_f = latent heat of fusion and L_v = latent heat of vaporization, what is the value of the ratio L_v / L_f for this substance?

A) 5.0
B) 4.5
C) 7.2
D) 3.5
E) 1.5