Answer
$D: (0,0) \\ G: (0,2a) \\ F: (b,2a) \\ E: (b,0)$
Work Step by Step
We know that any vertex on the x-axis has a y coordinate of 0, and we know that any coordinate on the y-axis has a x coordinate of 0. Thus, we write 0 where appropriate. We now assign a value of $2a$ for any value that has a height the same of that of the coordinate with a value of $2a$. Finally, we fill the remaining blanks by assigning a value of b for the x-value of the two coordinates that have the same x value. This gives:
$D: (0,0) \\ G: (0,2a) \\ F: (b,2a) \\ E: (b,0)$
