Place the arch at the top of the window and mark both contour of the arch with a pencil.
![Step1Wings2](http://artmoulding.com/wp-content/uploads/2017/03/Step1Wings2.png)
Place the side trims at the sides of the window and mark the countor of the trims.
![Step2Wings2](http://artmoulding.com/wp-content/uploads/2017/03/Step2Wings2-1.png)
Mark the intersection of the lines that were drawn before for the arch and trims.
![Step3Wings](http://artmoulding.com/wp-content/uploads/2017/03/Step3Wings.png)
Place the arch on top of the window again and mark the join lines.
![Step4Wings2](http://artmoulding.com/wp-content/uploads/2017/03/Step4Wings2.png)
Place the trims on the side of the window again and mark the join lines.
![Step5Wings2](http://artmoulding.com/wp-content/uploads/2017/03/Step5Wings2.png)
Cut the arch and the trims along the join lines that you marked previously and glue them to the wall.
![Step6Wings](http://artmoulding.com/wp-content/uploads/2017/03/Step6Wings.png)