$--$ Each question should be answered with only one SQL statement.

$--$Q$1)$ For each department, retrieve the department number,

$--$the number of employees in the department and

$--$their average salary in the department.

$--$ then order the result by the average salary in decending order.

$--$ output only departments that have the average salary higher than $50000.$

$--2)$ Retrieve the first name, last name, project name, and

$--$ weekly work hours per project of each employee

$--$ who works for department "Research."

$--$ Display the output in the descending order of last name and

$--$ then the ascending order by project name.

$--3)$ Retrieve the first name and last name of manager

$--$ who are managing department$($s$)$ located in "Houston"