The vertices of abc are a(-5,4), b(-2,4), and c(-3,2). if abc is reflected across the y-axis to produce the image a'b'c', find the coordinate of the vertex a'.

Remember that it is in form (x,y)
reflected across the y axis means that x value is multiplied by -1 and the y value remains the same

think of it like you are standing in front of a mirror and you see yourself 'in' the mirror
immagine that it wasn't a mirror and it was a door
lets say that someone was looking from the side and saw the door in the middle and you on either side
that is reflected across the y axis with the door being the y axis

so we are only concerned with the vertex A
A=(-5,4)
we must multiply the x value by -1 so
(x,y)
x=-5
-5 times -1=+5
the point is (5,4)