3.(25%) Air flows at a rate of 3kg/s through a smooth contraction in a pipe with negligible friction losses (the pipe diameters are D, = 0.4m and D, -0.2m. respectively). The pressure difference between the two sections is measured by two tubes connected to a water manometer. Calculate the height Ah measured between the two vertical tubes (assume air density is 1.22 kg/m' and water density is 1000 kg/m).