From 2004 to 2005 the sales of a book decreased by 80%. If the sales in 2006 were the same as in 2004, by what percent did they increase from 2005 to 2006?

প্রশ্নঃ From 2004 to 2005 the sales of a book decreased by 80%. If the sales in 2006 were the same as in 2004, by what percent did they increase from 2005 to 2006?