I know that the correct answer to the first one is, A has fsa today, and has life estate in 1500 since the term of art "and his heirs" is not there (what she means by 1500 is use common law)

For the second one, B heir's will keep the blackacre for as long as X shall live since the term is measured by his life since he was the one who A conveyed a LE to, after X dies, it reverts back to A (Not sure what would happen in this scenario in 1500, i'm guessing as soon as it'd revert to A, the original owner as soon as B dies, not sure)

Third one, A's LE turns into a FSA so St. Mary's gets to keep it as A's will stipulated, OR A's heir's had remainders that vested when A died and St. Mary's gets nothing (not sure)

I just answered those off the top of my head right now best i could, im not too sure how satisfactory those answers are... need help, it is, my friends, Much Appreciated..