It would be best to label the points if your turning it in. It can help people easily identify the points you've plotted.
From the looks of it, your equation is good.
The base is good and your math is right, but where did you get your height from?
If you count from point R up to line PQ you get 5 as the height.
I understand miscounting's a thing, no worries.
So if we input the correct height, we get A = 1/2 (3)(5)
1/2 * 15
7.5
The area of the polygon is 7.5 units.
I hope that helps and if you ever need any more help don't be afraid to reach out!