A system consists of nitrogen (N2) in a piston-cylinder assembly, initially at p1 = 20 lbf/in^2 , and occupying a volume of 2.5 ft^3. The nitrogen is compressed to p2 = 100 lbf/in^2 and a final volume of 1.5 ft^3. During the process, the relation between pressure and volume is linear. Determine the pressure, in lbf/in^2, at an intermediate state where the volume is 2.1 ft^3 , sketch the process on a graph of pressure versus volume.