Chinese Year on a Postmark
It's most probably written vertically, right to left:

七年八月十一 Year 7, Month 8, 11(th day). 1938/8/11 (Year 1 is 1932).

No idea what the 九/9 at the end stands for. 

EDIT

As Wang Dingwei says, Henan wasn't part of Manchukuo. So year 7 is probably 1918. 紀元轉換