A pressure measure at the top of an oil well 18,000 ft deep registers 2,000 psig. The bottom 4,000-ft portion of the well is filled with oil (\rho = 43.68 lbm/ft3). The remainder of the well is filled with natural gas (T= 60 °F, compressibility factor Z= 0.8, and specific gravity s = 0.65, meaning that the molecular weight is 0.65 times that of air). Compute the pressure (psig) at (1) the oil/gas interface, and (2) the bottom of the well.