Need Help To Identify

I found a nice stack of these in my collection does anybody know what they are?



it is both sides

Tina, they are the German version of a
FDC sheet. Here is a definition from a
German site.

A Ersttagsblatt (short: ETB) is a sheet, provided with a stamp, cancelled by the post office and, which carries a Ersttagsstempel, thus on the first validity day.Also has descriptions of motive and technical data on reverse. In the Philatelie ETBs are separately evaluated and to reach often a multiple at value of the respective stamp.

Thank you meostamps so how or where would I find the value of these at?