A solenoid is designed to produce a magnetic field of $0.0270 \mathrm{~T}$ at its center. It has radius $1.40 \mathrm{~cm}$ and length $40.0 \mathrm{~cm},$ and the wire can carry a maximum current of 12.0 A. (a) What minimum number of turns per unit length must the solenoid have? (b) What total length of wire is required?