We are given the preimage points and the mapped points (image):
A(-6, -2) A'(-6, 2)
B(-3, -6) B'(-3, 6)
C(-2, -2) C'(-2, 2)
We can see the x-coordinate of the preimage and the image are the same, but the y-coordinate is negated (or inverted).
This rule corresponds to a reflection across the x-axis.
Thus, the transformation is a reflection across the x-axis and the rule is to negate the value of the y-coordinate of each point, but leave the x-value the same.