请教一道数学

gpc7109

Q29:
The toll for crossing a certain bridge is $0.75 each crossing. Drivers who frequently use
the bridge may instead purchase a sticker each month for $13.00 and then pay only $0.30
each crossing during that month. If a particular driver will cross the bridge twice on each
10
of x days next month and will not cross the bridge on any other day, what is the least
value of x for which this driver can save money by using the sticker?
A. 14
B. 15
C. 16
D. 28
E. 29

看了半天也没找到思路,请NN人帮助.谢谢了.

missalcohol

请问是选E么？

korea_univ

13+0.3*2x小于等于0.75*2x  解出x大于等于14.4，所以是B 15

missalcohol

 那么这个条件 If a particular driver will cross the bridge twice on each 10 of x days next month， 怎么用呢？

gpc7109

答案是B .Thanks