you just need to plug in the values.
Take, Ln P_v = -delta_vap H / RT + C ( constant of integration)
plug in the coordinates of the trip pt and normal boil pt to solve 2 eq's of 2 uknowns . u find delta_vap H. Then ofcourse delta H sublimation = fusion + vaporization. You find the changei n enthalpy of fusion.