$4.$ A wing of a small aircraft is rectangular in plan having a span of $10$ m and chord of $1\mathrm{.}2$ m $.$ In straight and level flight at $\backslash (240\backslash$mathrm$\{$~km$\}/\backslash$mathrm$\{$h$\}\backslash )$ the total aerodynamic force acting on the wing is $20$ kN $.$ If the lift to drag ratio is $10,$ calculate the coefficient of lift and the total mass the aircraft can carry. Assume air density is $\backslash (1\mathrm{.}2\backslash$mathrm$\{$~kg$\}/\backslash$mathrm$\{$m$\}3\backslash ).$

$($ans:$0\mathrm{.}622,2028\mathrm{.}5)$