The water in the tank is pressurized by air, and the pressure is measured by a manometer as shown in the figure below. Determine the gauge pressure of air in the tank (in psi units) if h1 = 20 cm, h2 = 15 cm, h3 = 35 cm and the atmospheric pressure is 1 atm. Take the densities of water, oil and mercury to be 1000 kg/m3, 920 kg/m3, 13,600 kg/m3, respectively.