CREATE TABLE table_18590048_1 (release_date VARCHAR, units_sold__in_millions_ VARCHAR)

What day did the platform sell 9.87 million units?
SELECT release_date FROM table_18590048_1 WHERE units_sold__in_millions_ = "9.87"
SELECT "release_date" FROM "table_18590048_1" WHERE "9.87" = "units_sold__in_millions_"