Answer:
select sum(HoursWorked)
from OWNER
where ExperienceLevel <> 'Junior'
group by ExperienceLevel
having count(*) >= 3
Explanation:
First use the sum function on HoursWorked column of OWNER table. Then put the required condition of not including employees with experience level of Junior. And then use group by function to bulk the results by experience level and group only results with equal to or more than 3 records.