Help!

[Marc Summers]

The slope of the hypotenuse of the right triangle is 3/8, or .375
The slope of the diagonal on the trapezoid (the longest side) is 2/5, or .4

This would NOT line up into a perfect rectangle, and as a matter of fact, if you look at the finished rectangle, you can barely see little misalignments on the corners and edges between the shapes. The fact that the slopes of the two edges I described are so close makes the difference on the diagram hardly noticable, but those tiny little differences are spread all over the whole "rectangle" to make it look like it could be counted as one.