Well you know that the amount of boys that voted for Danny has to be 123 - 55, so you do that and get 68, then the ratio of girls to boys is 55:68, and that can't be simplified anymore because 55 has factors of only 1, 55, 11, and 5, and that doesn't get you anywhere.
This ratio compares part-to-part, or the number of votes from girls to the number of votes from boys. If 123 people voted for Danny and 55 of those votes were from girls, then 68 votes were from boys. The ratio would be 55:68.
