Break the polygon into two sections.
You could cut it into a rectangle and then a square.
In order to find the area of a rectangle you multiply length times width
You get- 87.5 yds squared
Then to find the area of a square it is side squared
You get- 56.25 yds squared
Add those together to get the full answer- 143.75 yds squared
It is kind of hard to completely explain through typing but I hope it helps in some way :)