What is the efficiency of a 10 ft, fixed pitch propeller, with a 30-degree blade angle at 0.75R, and performance as given in figure 2.25, when rotating at 1,950 rpm, the airplane having an airspeed of 150 knots at sea level?

What is the efficiency of a 10 ft, fixed pitch propeller, with a 30-degree blade angle at 0.75R, and performance as given in figure 2.25, when rotating at 1,950 rpm, the airplane having an airspeed of 150 knots at sea level?