Answer
$P(E)=0.25$
If the husband and wife have 4 children, we would expect that one will have sicklecell anemia.
Work Step by Step
Event = "the offspring will have sicklecell anemia" = {ss}. So $N(E)=1$
The sample space: S = {SS, Ss, sS, ss}. So, $N(S)=4$
$P(E)=\frac{N(E)}{N(S)}=\frac{1}{4}=0.25$
