Need to find X in SHA1[(AES-128(X)]

Hi

This is the problem I am trying to solve:

Please take you birthday (day and month) in hexadecimal form. Find message X that SHA1[(AES-128(X)]=0x[18 arbitrary bytes][day][month]. AES key is 0x00000000000000000000000000000000.
For example, if you birthday is January 10th, please find X, that SHA1[AES-128(X))]=0x[18 arbitrary bytes]1001.

I am quite noob to working with problems like this so I was hoping someone could explain how exactly am I supposed to work this out.

Sorry for the vague question but I don't really know what to exactly ask either.
Thanks!