The image for this question can be found at: screenshots(dot)firefox(dot)com/AsFVDd1o7hceJtQT/null

The square has side length 12 and the area of the blue region is 12

What is the combined area of the yellow regions?

The altitude of the large yellow area is 12, the side of the square.

So, if you folded the small triangular area which includes the blue, the area outlined by the large yellow triangle would be
12*12/2 = 72
subtract the blue twice (once in its present location, and again after having been folded to the left), and the remaining yellow is 72-2*12 = 48