Help me don't understand how to see if the beam is aligned using string! picture

[gasto]

do you mean 4 meters towards the wall and 3 meters out as the picture shows?
I still don't quite understand how I'm supposed to get that

 

[PCLarsson]

Now you are close.

Let the distance and points along the house walls be fixed. Then adjust the point closest in the image so that there is 5 meters between the point furthest to the right along the house wall and the point closest in the image. However, the distance between the point closest in the image and the point furthest to the left along the house wall must remain constant at 4 meters.