Air at 40°C flow steadily through the pipe shown in Fig. 1 below. If P1 = 40 kPa (gage), P2 = 10 kPa (gage), D = 3d, Patm ≅ 100 kPa, the average velocity at section 2 is V2 = 25 m/s, and air temperature remains nearly constant, determine the average speed at section 1. ​