In the xy-plane, the region y > 0 has a uniform magnetic field B₁k^ and the region y < 0 has another uniform magnetic field B₂k^. A positively charged particle is projected from the origin along the positive y-axis with speed v₀ = π m s⁻¹ at t = 0, as shown in the figure. Neglect gravity in this problem. Let t = T be the time when the particle crosses the x-axis from below for the first time. If B₂ = 4B₁, the average speed of the particle, in m s⁻¹, along the x-axis in the time interval T is __________.