求解两道数学题

AARONALAN

今天做了一套GWD的题，其中有两道题，求出的结果和答案不符，但又不知错在哪！忘高手，牛人指教。
Q22:

How many 4-digit positive integers are there in which all 4 digits are even?



A.625

B.600

C.500

D.400

E.256
答案是500
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 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

答案是15


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 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

答案是15