Total votes for...
Wallace - 11
Casey - 8
Whitney - 8
Lisle - 8
with the overall total number of 35 votes. So from this data, it would appear that Whitney has a [tex]\dfrac8{35}[/tex] probability of winning.
From a student body consisting of 420 voters, you would expect approximately [tex]420\times\dfrac8{35}=96[/tex] votes to go to Whitney, and so the answer is D.