The question: 1 kg of a fluid expands reversibly according to a linear law from 4.2 bar to 1.4 bar;the initial and final volumes are 0.004m^3 and 0.2m^3. The fluid is then cooled reversibly at constant pressure,and finally compressed reversibly according to a law pv=constant back to the initial conditions of 4.2 bar and 0.004m^3. Calculate the workdone in each process and the net work of the cycle. Sketch the cycle on a p-v diagram.
My problems:1 I don't understand what it means to expand according to a linear law and at pressure. What relationship am I to use. Am really confused. Please HELP!!

This means that if you plotted the change in volume while the pressure is changed as in the first statement, you will get a straight line.

Also meaning that

where k and c are constants, V is the volume of the fluid and P is the pressure.

Thanks...