There is some spurious, unnecessary information included in the question. It matters not that the the measurements are in cms to answer the question asked. They could have been in inches or cubits and it would not have affected the solution. Other than that the one unstated assumption is that the shape is on a planer surface. If it had been on some kind of curved surface then that would make it an "impossible" question. In fact, the question would probably need to be "Show that the shape must be on a planer surface for it to hold that the angles shown are indeed right-angles".