wavelength of an electron l = h/p = 8.7 x 10^-11
h --> Planck's Constant
m --> Momentum
Wavelength l = h/p = h/mv = > v = h/(m*l)
From the given values,
m = 9.1 x 10^-31 kg
l = 8.7 x 10^-11 m
h = 6.626x10^-34 Js
v = 6.626x10^-34/ ((9.1 x 10^-31)*(8.7 x 10^-11))
The velocity of electron v = 8.37x10^6 m/s