So if RL is "Roof Load", W is "width of the bay window's opening in the wall", D is "depth of the bay window, or how far the window sticks out past the rest of the wall", and P is "the pitch angle of the roof, covering the two-floor building, where the bay window is on the first floor", then your eqn is
. . .
And you're using W = 3, D = 1, P = 45 degrees. Then
. . .
There's lots of fine print on the page of info, saying how this is simplified and is only good for a very specific situation. But I think they made a mistake.