m = 4/5 for the perpendicular line
m = -5/4 for the parallel line
y = -5/4x + 3
for the line above, m = -5/4
The line parallel to this line would have exactly the same slope m = -5/4
The line perpendicular to this line would have a slope equal the inverse with the opposite sign
m = -5/4
So m = (1/(5/4)) is the slope of the m for the perpendicular line
m = 4/5
