Get ya close...
Here's what usually gets me close...
A flying wing should be 17% or thereabouts...(square wing)
So, I just make it a right triangle and double the distance of what 17% would be if it were a square or rectangle. With the given 45 degree sweep...17% is 6.8 inches on your 40 inch chord ..
doubled gives you...
13.6 inches MINUS what you would have on the nose if it were a point...if 45 degrees... would be 2.5 inches or so...so subtract that from the 13.6 and you get about 11 inches from the nose...
Hope that helps....
CrazyHerb