Fourier transform ion cyclotron resonance mass spectrometry yields the highest resolution mass spectra. As an example of the high resolution attainable by this technique, consider the case of molecular ions of two polypeptides (each polypeptide being composed of seven amino acids) differing in mass by 0.00042 Da that were separated with a 10% valley between them. The ions each have a mass of 906.49 Da and a width at half-height of 0.00023 Da. Compute the resolving power by the 10% valley formula and by the half-width formula.