An industry consists of 30 firms, and the top 5 firms have annual sales of $5 million, $4.1 million, $3.3 million, $1.6 million, and $1 million, respectively. The next 25 firms have combined annual sales of $9 million. Given this information, the four-firm concentration ratio is approximately _________________ percent. (Round your answer to nearest 1 decimal place)