Question: Find the total hours of the projects that scientists named Michael Rogers or Carol Smith are assigned to.
SQL: SELECT sum(T2.hours) FROM assignedto AS T1 JOIN projects AS T2 ON T1.project  =  T2.code JOIN scientists AS T3 ON T1.scientist  =  T3.SSN WHERE T3.name  =  'Michael Rogers' OR T3.name  =  'Carol Smith'