An electron with a speed of 3.0 × 10⁶ m/s collides with an atom which has the following energy levels: n₁ = -24.6 eV, n₂ = -5.4 eV, and n₃ = -2.4 eV. The atom emits a 619.9 nm photon after the collision. Ignoring the atomic recoil, since the atom's mass is significantly larger than the electron's mass, determine what the electron's final speed will be. Note that the photon energy ≠ collision energy.