Hi, I have uploaded a picture that shows my question. Can someone give me a direction, I have been sitting on this for hours, I couldn't do it. I tried to use the fact that P and Q are invertible and tried to find A in block matrix and maybe somehow get something, I am trying random things, I don't really know what I am doing, so can someone give me a subtle hint, by that I mean a hint that doesn't show me what to do in every step of the solution but rather gives me a first step how to start solving it. Thank you.