OK, here's method 2. This method is also pretty easy, and is especially easy with a 9:12. This method uses similar triangles.

It helps to draw a little cross section of the plate (this one is by no means to scale. There's a bunch of triangles in there, and if you can solve for some unknowns, then you can get all of the numbers that you need.

You'll need the diagonal or hypotenuse of the roof pitch triangle. The rise is 9, the run is 12 (or maybe 10 if you're in Europe or Japan), so in this case the diagonal (also called the rafter length) is conveniently 15. It's a 3/4/5 triangle. If it's not, then you can use the Pythagorean theorem to solve for it.

You want to know 'x' in the drawing, which is equivalent to the hypotenuse, or 15. We know the rise of that shaded triangle, as it's 2", which is equivalent to the rise of the roof pitch (9). Cross muliply, you get 3.33

You want to solve for 'y', which is our vertical drop, that's also equivalent to the hypotenuse (15). This time our known value is the base of that triangle, which is 2", the same as our 12. Cross multiply, you get 2.5".

These numbers can be checked with another one of the methods.

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