The coordinates of the triangle are:
[tex]\begin{gathered} A\to(-1,5) \\ B\to(-4,4) \\ C\to(-3,1) \end{gathered}[/tex]So if we made a reflection over the y axis we will cahnge the sign of the x coordinate so:
[tex]\begin{gathered} A\to(-1,5)\to(1,5) \\ B\to(-4,4)\to(4,4) \\ C\to(-3,1)\to(3,1) \end{gathered}[/tex]