Planck's Constant Is 6

Multiple Choice

Planck's constant is 6.6 * 10^-34 J·s and the proton mass is 1.7 * 10^-27 kg.The speed of a proton whose de Broglie wavelength is 4.0 * 10⁷ m is

A) 7.8 * 10^-20 m/s.
B) 9.9 * 10² m/s.
C) 1.9 * 10⁶ m/s.
D) 3.9 * 10⁶ m/s.