What are the total hours per week students under the age of 20 played games?
SELECT sum ( hoursperweek )   FROM Sportsinfo AS T1 JOIN Student AS T2 ON T1.StuID   =   T2.StuID WHERE T2.age  <  20
total hours = SUM(hoursperweek); students under the age of 20 refers to WHERE age < 20; per week played games refers to the context of hoursperweek in the domain of gaming or sports activities; joining tables Sportsinfo and Student refers to linking game playing time with student information based on student ID (StuID).