From Mechanics

As the parachutist is falling vertically (in other words in a straight line) and at constant speed, her velocity is constant. This means the forces acting on her must have zero sum.

Taking upwards as positive,

\displaystyle \uparrow :\quad F-mg=0

\displaystyle F=mg=80\times 9\textrm{.}8=784\ \text{N}