Question

I thought it was (6,-4) but that isn't a choice.

Answer 1

To make a reflection over the y-axis of any point on the coordinate system, what you have to do is change the sign of the x-coordinate of the point, leaving the y-coordinate the same, following the rule:

$(x,y)\to(-x,y)$

Triangle DEF was reflected over the y-axis to triangle D'E'F'

The coordinates of point F are F(6,-4)

Reflect the coordinates of F using the rule:

$F(6,-4)\to F^{\prime}(-6,-4)$

The coordinates of F' are (-6,-4)