[求助]请教一道简单的蓝皮书18题

18. Last year mrs long received $160 in dividends on her shares of company X stock, all of which she had held for the entire year. If she had had 12 more shares of the stock last year, she would have received $15 more in total anumal dividends. How many shares of the stock did she have last year?

A. 128

B. 140

C.172

D.175

E.200

答案给的是A，但我怎么也算不出来， 请帮帮我，先谢了。

谢谢。