Welcome to Physics Forums.
Can you try stating the problem better? Where is axis AA'? Is it in the plane? Or coming up vertically out of the plane? Guessing from the provided diagram, it is in the plane and is the y-axis over on the left
Can you label the drawing better? Where are points a, b and c? It looks like it's "a" up top, "b" on the right and "c" on the lower left.
Do you have a strategy in mind? It looks like you are busy calculating angles. I don't think the angles are going to do you any good. Have you thought about the parallel axis theorem, for instance? How might you go about applying that?