Simplify the following text for a Grade 6 native English-speaking person.
Original: Since her 1998 debut with the single `` Poker Face '' , Hamasaki has sold over 50 million records in Japan , making her the best selling solo singer in Japanese history and ranking her among the best-selling singers in the country .
Simplified: Since she debuted in 1998 with `` Poker Face , '' Hamasaki sold more than 50 records in Japan . This puts her as one of the highest ranking singers in the country .