This passage will probably get a 3 in the real test although 3.5 is possible. You fail to include enough details and examples when talking about why increasing salary does not make the best solution. In fact, my suggestion is to introduce other ways to improve education quality that are more important than paying teachers more. Remember, we put a big weight on details and examples when grading.
A minor thing I want to mention is that sentences like "There is no doubt that it is an effective way to improve education by raising teachers’ salaries." are judged as redundant in our grading process so you may want to use such convoluted structure. A possible way to express your original sentence is "Undoubtedly, raising teachers' salaries is an effective way to improve educatioin quality". In fact, this is a common problem we find in many test takers' passages even in those getting 5. What we are really looking for is an efficient use of different sentence structures.