Right △abc has coordinates a(-7, 3), b(-7, 10), and c(-1, 3). the triangle is reflected over the x-axis and then reflected again over the y-axis to create △a'b'c'. which are the coordinates of vertex a'?

X-axis = A (-7,-3) B (-7,-10) C (-1,-3) first they changed to the x-axis which is this. Just so you know on the x-axis the x-axis stay and the y-axis changed which is this.
When they reflect again on the y-axis the verter of A' is
A' (7, 3) = answer
On the y-axis the y- axis doesnt change but the x-axis changed.
Hope this help!

21/2 or 5/2

Bis the answer! hope this