To deal with
a tailwind, enter the graph at the nautical ground miles figure and go
vertically up to the REF LINE (as you would with a headwind), then, instead of
following the curved lines up to the headwind figure, follow the lines
backwards until you get to the intersection with the tailwind component (-50 in
this case) and then draw the line vertically upwards from there until the
intersection with the brake release weight required.
The rest is
the same as for the headwind component calculations.