The answer for this problem would be: Assuming non-relativistic momentum, then you have: ΔxΔp = mΔxΔv = h / (4) Δv = h / (4πmΔx) m ~ 1.67e-27 h ~ 6.62e-34,Δx = 4e-15 --> Δv ~ 6.62e-34 / (4π * 1.67e-27 * 4e-15) ~ 7,886,270 m/s ~ 7.89e6 m/s That's about 1% of the speed of light, the assumption that it's non-relativistic.
