x, y and z can complete a piece of work in 9, 18 and 24 days respectively, They started working together, but y and z left work 3 days and 2 days before the completion of the work respectively. What was the ratio of contribution of y to that of z in the completed piece of work?

• A. 4 : 5
• B. 3 : 2
• C. 2 : 3
• D. 1 : 1