Explanation:
the slope is always the ratio "y coordinate change / 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