I WILL GIVE BRAINLIEST TO WHOEVER IS CORRECT

Answer:
(2a,a)
Step-by-step explanation:
We know that the longer side (the length) is twice the shorter side (the height). So the x-coordinate will be twice the highest y-coordinate. The highest y-coordinate is a, so the furthest x-coordinate will be 2a. The top right vertex lies on the same y-coordinate as the top left, so the y-coordinate will also be a.
(2a, a) is the answer.
I really hope this helps you =)