I want to believe you mean we find the vertices of the vertices P(−3, −4), Q(3, 4), and R(−6, −3) under a reflection on X=0.
Line X=0 is the y-axis. So for reflection under this axis the y coordinates does not change but the x coordinates only change the sign.
For example, for a point A(x, y) its image under RX=0, A'(-x,y)
A(x, y) ⇒ A'(-x, y)
P(−3, −4) ⇒ P'(3, -4)
Q(3, 4) ⇒ Q'(-3, 4) and
R(−6, −3) ⇒ R'(-6, -3)
