Well, remember, to melt something, we actually have to input energy. And when we melt something by inputting energy, the energy is breaking the intermolecular bonds. And what that implies is the intermolecular bonds in the longer fatty acid are stronger than intermolecular bonds in that shorter fatty acid. The question is, why is that so? Well, what types of bonds do we have between two non polar molecules? Well, typically, the bonds are London dispersion forces.