a. No, it is not a sex-linked trait.
b. The distribution shows that it is a recessive trait, because the offspring can present the trait even if both parents doesn't present it. If it was X-linked, the number 3 would have to present the trait. As it is a male, it would have to pass the X with the trait on for his daughter (10), as well as the mother (4) would have to pass it on as well. But the daughter (10) presents it and the father doesn't, showing that it's not X-linked. If it was Y-linked, females would never show the trait, but they do.
c. There are three generations. The first is represented by number 1, 2, 3 and 4. The second is represented by the numbers 5, 6, 7, 8, 9, 10, 11. The third is represented by the numbers 12, 13 and 14.