please i need a cleat steps to understand the solution

Example 7.1 Air and water flow at 8103kg/s and 0.4kg/s upwards in a vertical, smooth-wall tube of internal diameter di=20mm and length L=1.3m. Using the homogeneous flow model, calculate the pressure drop across the tube (neglecting end effects). The fluids are at a temperature of 20C and the expansion of the air may be assumed to be isothermal. The exit pressure is 1 bar. Calculations The required equation for the pressure gradient is dxdP=(di2fG2V+G2VLGdxdw+Vgsin)/(1+G2wdPdVG) There is no change of quality, so dw/dx=0. The following values are readily calculated