Air ($\rho$=$1.2 \: kg/m^3$ and kinematic viscosity, $V$ = $2 \times10^{−5}$ $m^2$/$s$) 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 $C_f=\dfrac{1.328}{\sqrt{Re_x}}$, the total drag force (in $N$) per unit width of the plate is _______