33. A project is completed in whole days when worked on in the order of Jia, Yi, Bing each working for one day. If the work is done in the order of Bing, Jia, Yi each working for one day, it will take 0.5 days longer than the original plan; if the work is done in the order of Yi, Bing, Jia each working for one day, it will take 1 day longer than the original plan. Yi alone can complete the project in 30 days. Jia, Yi, and Bing working together need $\qquad$ days to complete the project.
answer: 7.5