请教一道JJ

100.   $1200 costs for the fist printing of 1000 copies of a certain book, $1000 costs for the second printing of 1000, then x dollar costs for the sequent per copy printing. Then $6587 (?) costs for the first printing of 7500 copies of the book, what x is?

0.80

0.85

0.89

0.91

0.92

不是很明白说什么

楼主再仔细读读，这是我的解法：

1200+1000+（7500-2000）*x=6587    x=0.8

供参考