Determine the work done by a 1-lb fluid system as it expands slowly within a piston-cylinder arrangement from an initial pressure and volume of 80 psia and 1 ft3, respectively, to a final volume of 4 ft3 in accordance with the following defining relations: (a) p = C; (b) pV =C; (c) pV1.4 = C; (d) pV2 = C; (e) p = - 20V + 100, psia.