Since your question has dollars in it, you would just forget about the dollars sign and divide like you would regularly, so 11.25 divided by 5 would be 2.25, so there's how you get your answer.
Just by eyeballing it EB is half of AB which looks like the same length of CD so you would times EB(5) by 2 to get the full length of CD which is 10 Hope it helps :)