An air-filled toroidal solenoid has a mean radius of 15.0 and a cross-sectional area of 5.02 (see the figure). The current flowing through it is 12.0 , and it is desired that the energy stored within the solenoid be at least 0.390 What is the least number of turns that the winding must have? Express your answer numerically, as a whole number, to three significant figures.