Answer: 43.3%
Steps:
List the votes in a table:
Vote
Candidate A 17
Candidate B 13
No Vote: 14 (34-30)
The fraction of the voters for candidate B is
13/(13+17)=0.4333...
This corresponds to 100*0.4333...=43.33...% and rounded to 43.3%
Note that the question asks for percentage of "voters" not "students"