Explanation:
a parallel line has the exact same slope.
for the slope of a perpendicular line (at a 90° angle) x and y trade places. and the sign of the slope flips.
remember, the slope is the ratio "y coordinate change / x coordinate change" when going from one point on the line to another.
so, we have 2 points on m : (-4, 5) and (8, 2).
going from the first to the second we see
x changes by +12 (from -4 to 8).
y changes by -3 (from 5 to 2).
the slope is then -3/+12 = -1/4.
the slope of the parallel line is also -1/4.
the slope of the perpendicular line is then +4/1 = 4.