²log81/8+2.²log2/3-2.²log3/4

²log81/8 + ²log(2/3)² – ²log(3/4)²
=²log 81/8.4/9 per 9/16
=²log 9/2.16/9
=²log 8
=²log 2³
=3.²log 2
=3.1=3