Explanation:
the slope is always the ratio "y coordinate charge / x coordinate change" when going from one point on the line to another.
so, when going from (-2, 1) to (4, -3)
x changes by +6 (from -2 to 4).
y changes by -4 (from 1 to -3).
therefore, the slope is
-4/+6 = -4/6 = -2/3