How many sales does game platform id 3871 make in Europe?
number of sales = multiply(num_sales, 100000); in Europe refers to region_name = 'Europe'
SELECT T2.num_sales * 100000 FROM region AS T1 INNER JOIN region_sales AS T2 ON T1.id = T2.region_id WHERE T1.region_name = 'Europe' AND T2.game_platform_id = 3871