Answer
The daughter has a 0% chance of having hemophilia, and a son has a 50% chance. The chance of 4 sons all having hemophilia is 1/16 or 6.25%.
Work Step by Step
Do a Punnett square, knowing that the woman must have her father's chromosome with a hemophilia allele (h), but her mother must have given her a normal allele (H) since the woman is unaffected. Her husband, normal, must be H-. Any daughter will get the father's normal chromosome, preventing her from having hemophilia, while sons will only have one of their mother's X chromosomes, 50% (1/2) of which carry the h allele. Four sons having hemophilia: $1/2^{4}$=1/16.
