He should place the picture at 6.75 inches from the edge of the wall.
Step-by-step explanation
According to the below diagram, O is the center of the wall and AB is the distance of the picture from the edge of the wall.
As the length of the wall is
inches or 31.75 inches , so the half length of the wall
inches.
Now, the length of the picture is
inches or 18.25 inches, so the half length of the picture
inches.
Thus,
inches
So, he should place the picture at 6.75 inches from the edge of the wall.