For each problem, What are the different names of staff members who can authorize closure!
select distinct t2.staff_first_name, t2.staff_last_name from problems as t1 join staff as t2 on t1.closure_authorised_by_staff_id = t2.staff_id
Also provide the product_ids!
select product_id, t2.staff_first_name, t2.staff_last_name from problems as t1 join staff as t2 on t1.closure_authorised_by_staff_id = t2.staff_id
Show me the product ids that have closure authorized by Ashley Medhurst!
select product_id from problems as t1 join staff as t2 on t1.closure_authorised_by_staff_id = t2.staff_id where t2.staff_first_name = "Ashley" and t2.staff_last_name = "Medhurst"
Of those, only those that were reported  by Christop Beege!
select product_id from problems as t1 join staff as t2 on t1.reported_by_staff_id = t2.staff_id where t2.staff_first_name = "Christop" and t2.staff_last_name = "Berge" intersect select product_id from problems as t1 join staff as t2 on t1.closure_authorised_by_staff_id = t2.staff_id where t2.staff_first_name = "Ashley" and t2.staff_last_name = "Medhurst"