I have a thin strip of paper 1 inch wide. I lay it out horizontally in front of me. Along the top edge I mark two points, at five inches and ten inches from the top left corner.
I fold the top left corner down and slightly to the right, such that the fold line passes through the bottom left corner of the strip and the ten inch mark on the top edge.
I then draw a straight line from the bottom left corner of the strip, passing through the new position of the five inch mark, and continuing on its shallow diagonal trajectory until it hits the top edge of the strip.
How far along is the point where the line meets the top edge?