An icon from the set Education Web Icons
DuckFiles
CC BY 3.0
<a rel="nofollow" class="external free" href="http://duckfiles.deviantart.com/art/Education-web-icons-set-Free-PSD-and-PNG-325020690">http://duckfiles.deviantart.com/art/Education-web-icons-set-Free-PSD-and-PNG-325020690</a>