Question: Calculate the GPA of the semester for Laughton Antonio.
SQL: SELECT CAST(SUM(T3.credit * CASE T1.grade WHEN 'A' THEN 4 WHEN 'B' THEN 3 WHEN 'C' THEN 2 WHEN 'D' THEN 1 ELSE 1 END) AS REAL) / COUNT(T3.credit) FROM registration AS T1 INNER JOIN student AS T2 ON T1.student_id = T2.student_id INNER JOIN course AS T3 ON T1.course_id = T3.course_id WHERE T2.f_name = 'Laughton' AND T2.l_name = 'Antonio'