Air (ρ = 1.2 kg/m³ and kinematic viscosity, ν = 2×10⁻⁵ m²/s) with a velocity of 2 m/s flows over the top surface of a flat plate of length 2.5 m. If the average value of friction coefficient is C_f = 1.328/√Re_x, the total drag force (in N) per unit width of the plate is ________