information from the "salaries" table regarding contracts from 66,000 to 70,000 dollars per year

SELECT   * FROM     salaries WHERE salary BETWEEN 66000 AND 70000; 

I think that above query will retrieve per contract. But your question is for per year. So I think that need to calculate for each year salary first based on contract period. Is it right?

The salary from employees table is based on contract which period is sometimes more than one year.

Dear instructor, looking forward your answer.............