hello guys, it is really late in my country and I cant really go to sleep without solving this question. My english is not so good so I hope that you understand every detail in the question if you dont understand something Ill be glad to hear from you. so here it is:

x is a liquid phase material that is in equilibrium with its vapor at a temperature T that equal to 306 Kelvin. Above the system (closed with the massless piston which is free to move along the cylinder and has a cross-sectional area of 30 cm) is placed an M weight with a mass of 151 kg. Beyond mass there is no additional force acting on the part of the environment. Also given is a phase diagram of material X in which points A and B are at a temperature of 350K. we change the temperature and pressure conditions in the system I described (with the piston) so that material X reaches point A. At a certain moment a weight is replaced over the piston in a smaller one (at once) and eventually the material reaches point B. The amount of heat absorbed by the system (in Joules) must be calculated When 2 mole x move from point A to point B. In the calculation a volume perceived by a liquid should be neglected compared to the volume of the gas (ideal gas). Also the volume of the liquid does not depend on the pressure.

Ive tryed several ways to solve it. If anyone can help me Ill be thankful.