A Hall-effect probe to measure magnetic field strengths needs to be calibrated in a known magnetic field. Although it is not easy to do, magnetic fields can be precisely measured by measuring the cyclotron frequency of protons. A testing laboratory adjusts a magnetic field until the proton's cyclotron frequency is 10.5 MHz. At this field strength, the Hall voltage on the probe is 0.543 mV when the current through the probe is 0.145 mA. Later, when an unknown magnetic field is measured, the Hall voltage at the same current is 1.734 mV.
A) Determine the strength of this magnetic field?