A toroidal solenoid has a radius of 0.12 m and a cross sectional area of 20×10^-4 m2. It is found that when the current is 20A, the energy is 0.1 J. How many turns does the winding have?

Along wire carrying a 4.2 a current perpendicular to the xy-plane intersects the x-axis at x=−1.7cm. a second, parallel wire carrying a 3.0 a current intersects the x-axis at x=+1.7cm. part a at what point on the x-axis is the magnetic field zero if the two currents are in the same direction? express your answer to two significant figures and include the appropriate units.