Write SQL query to solve given problem: Give the grade score for Rik Unsworth in "Computer Network".. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CASE grade WHEN 'A' THEN 4 WHEN 'B' THEN 3 WHEN 'C' THEN 2 ELSE 1 END AS result FROM registration WHERE student_id IN ( SELECT student_id FROM student WHERE f_name = 'Rik' AND l_name = 'Unsworth' AND course_id IN ( SELECT course_id FROM course WHERE name = 'Computer Network' ) )