Answer: (D) 50
Any rectangle is also a parallelogram (but not the other way around). So AB is parallel to CD. The angles BAC and ACD are alternate interior angles that are congruent due to the parallel sides mentioned.
(angle BAC) = (angle ACD)
3x+4 = x+28
3x-x = 28-4
2x = 24
x = 24/2
x = 12
So,
angle BAC = 3x+4 = 3*12+4 = 40 degrees
and
angle CAD = 90 - (angle BAC) = 90 - 40 = 50 degrees
With any rectangle, the four interior angles are always 90 degrees. So that's why angles BAC and CAD add to 90.