A current-carrying solenoid is 20 cm long and is wound with 1600 turns of wire. It produces a magnetic field of 6.010 4 T at the solenoid’s center.

A current-carrying solenoid is 20 cm long and is wound with 1600 turns of wire. It produces a magnetic field of 6.0×10−4 T at the solenoid’s center.
-How long would you make the solenoid in order to produce a field of 9.0×10−4 T at its center?
-Adjusting only the windings, what number would be needed to produce a field of 1.2×10−3 T at the center?
-What current in the solenoid would be needed to produce a field of 1.2×10−3 T but in the opposite direction?