An air-filled toroidal solenoid has a mean radius of 14.7 cm and a cross-sectional area of 5.02 cm2 . The current flowing through it is 12.5 A , and it is desired that the energy stored within the solenoid be at least 0.394 J . Average radius ra cross-sectional area Aa. What is the least number of turns that the winding must have?
Express your answer numerically, as a whole number, to three significant figures.