Could you show how far you've got yourself?
I think I atleast got the idea how you calculate the molecular mass, but I think I either made false assumptions or just miscalculated.
Things that bother me:
The acid being the form H2X, suggests that it's diprotic, but I assumed that it is monoprotic, as I didn't have Ka(HX-).
The answer I got is quite unbelieveable to me atleast
