Answer:
slope = - 
Step-by-step explanation:
The equation of a line in point- slope form is
y - b = m(x - a)
where m is the slope and (a, b) a point on the line
y - 3 = 3 (x + 4) ← is in point- slope form
with slope m = 3
The diagonals of a square are perpendicular to each other.
Given a line with slope m then the slope of a line perpendicular to it is
= -
= - 
Thus the slope of FH is - 