\(135|3\\.\ 45|
3\\.\ 15|3\\.\ \ 5|5\\.\ \ 1|\\135=\fbox3\cdot\fbox3\cdot\fbox3\cdot5\\\\81|3\\27|3\\.\ 9|3\\.\ 3|3\\.\ 1|\\81=\fbox3\cdot\fbox3\cdot\fbox3\cdot3\\\\the\ highest\ common\ factor\ of\ 135\ and\ 81\\\\=\fbox3\cdot\fbox3\cdot\fbox3=\boxed{\boxed{27}}\)
