Answer: It will take 30 days to complete this project alone.

(2), (20×2-35)÷ 1=5 (days) or (35-30× 1) ÷ 1 = 5 (days)

A: Then Project Team B will cooperate for at least 5 days.

Analysis (2): Team A spends 1 10,000 yuan more than Team B every day. It can be assumed that team A needs to spend 20× 2 = 400,000 yuan to complete all the * *, but the actual cost does not exceed 350,000 yuan, that is, at least 50,000 yuan is used less. However, team B spends less 10000 yuan per construction day than team A, so team B needs to construct 5 1 = 5 (days). In other words, team B will cooperate for at least five days.

In addition, it can also be assumed that team B needs 30×1= 300,000 yuan to complete all * *, but the actual cost does not exceed 350,000 yuan, that is, at least 50,000 yuan is used more. However, Team A uses 1 ,000 yuan more than Team B every construction day, so Team A works for 5 days. In other words, team B will cooperate for at least five days.