From the data sheet, the de Broglie wavelength, 𝜆 = h/p = h/(mv)
The electron wavelength equals the proton wavelength so: 𝜆e = 𝜆p
So: h/(meve) = h/(mpvp)
meve = mpvp
so the electron speed, ve = (mpvp)/me
From the data sheet, the rest mass of an electron and a proton respectively are: me = 9.11x10-31kg, and: mp = 1.67x10-27kg
Subbing these values along with the proton speed from the question gives:
ve = (1.67x10-27 x 3.1x104)/( 9.11x10-31)
ve = 5.7x107ms-1