How do you reflect a figure across the x axis

To reflect a figure across an axis means to mirror it.  This means that that triangle in the picture must be mirrored across the x - axis.  Since your problem is only asking for the coordinate of H, this will take much less time.

Since this is getting reflected across the x - axis, the x value of the coordinate is going to stay the same.  So we know then that the x value is going to be -4.  Now all you have to do is find the y value, but switch the sign.  The y value of H is 5, so the reflected value will be -5.

With this info we can figure that the coordinate will be (-4,-5), meaning the answer is C!

Hope this helps! :)