If,
as in this question, they ask for the "landing distance" then this is
the graphical distance corrected for slope and surface condition.
If they ask for the "landing distance required" then we must multiply
the graphical solution corrected for slope and surface condition by 1.43. This
is the safety factor required by the regulations that a prop a/c must land and
stop within 70% of the LDA or a factor of 1.43