A strip of three rectangles has one long diagonal from its bottom-left corner to its top-right corner. How many quadrilaterals are there in the figure?

Rectangles: 3 + 2 + 1 = 6. The diagonal cuts each of these rectangles; it leaves four-sided pieces in all except the whole strip (cut corner to corner): 1 in the left one, 2 in the middle one, 1 in the right one, and 1 in each of the two double ones, 6 more. Total $6+6=12$.