你能告诉我我的Python脚本有什么问题吗？（2.7.14）

Question

当我输入30时，它说它不正确，我做错了什么？

from datetime import datetime
now = datetime.now()
print '%s/%s/%s %s:%s:%s' % (now.year, now.month, now.day, now.hour, now.minute, now.second)
print raw_input('Welcome, first you need to confirm you can do math. Press ENTER to continue.')
answer = raw_input("What is 9 + 21?:")

if answer == 30:
    print 'Access granted.'
else:
    print 'Incorrect.'