An electron is ejected from a metal with a velocity of 6.7 × 10⁵ m/s. If the metal has a threshold frequency of 1.5 × 10¹5 Hz, what was the wavelength of the incident photon?

a) 4.4 × 10⁻10 m
b) 2.2 × 10⁻10 m
c) 1.5 × 10⁻10 m
d) 6.7 × 10⁻10 m