Answer:
R(-4g, 0)
Explanation:
Since the trapezoid is isosceles, point R is as far to the left of point M as point O is to the left of point H. That distance is g, so we need to add -g to the x-coordinate of M to get the x-coordinate of R. The y-coordinate of R is the same as the y-coordinate of H, 0.
Point R is (-4g, 0).