Question

The price, $C, of printing n copies of a book is partly constant and varies partly as n. The selling price of each copy of the book is fixed as $b. If 630 copies were printed and sold, there would be a loss of 10%. If 980 copies were printed and sold, there would be a profit of 12%. How many copies would have to be printed and sold in order to break even (i.e. neither gain nor lower)