4 Answers

12/40 for A
18/40 for B
10/40 did not vote  (12 + 18 = 30. 40 - 30 = 10) 
To find the percentage who voted for candidate "A", divide 12 by 40.  The answer is .3 or 30%
To find the percentage who voted for candidate "B", divide 18 by 40.  The answer is .45 or 45%
To find the percentage who did not vote, divide 10 by 40. The answer is .25 or 25%. 
30% + 45% + 25% = 100%

Which expression? I'm assuming by expression you mean the answer in characters. 30%. 

Sorry, math class for me was over 30 years ago. I do not recall what wording like "expressions" in math means. 

The lesser nomie,

The expression is that the majority   voted for candidate B  . Why is that same question being asked over and over ?