What is the average fastest lap speed in race named 'Monaco Grand Prix' in 2008 ?
SELECT avg(T2.fastestlapspeed) FROM races AS T1 JOIN results AS T2 ON T1.raceid = T2.raceid WHERE T1.year = 2008 AND T1.name = "Monaco Grand Prix"
average fastest lap speed = AVG(fastestlapspeed); race named 'Monaco Grand Prix' in 2008 refers to year = 2008 AND name = 'Monaco Grand Prix';