A closely wound, circular coil with radius 2.40 $\mathrm{cm}$ has 800 turns. a) What must the current in the coil be if the magnetic field at the center of the coil is 0.0580 $\mathrm{T}$ ? b) At what distance $x$ from the center of the coil, on the axis of the coil, is the magnetic field half its value at the center?