Если правильно понял:
1) в степени 2-log6 3
2=log6 36
log6 36-log6 3 = log6 36/3 = log6 12
2) 6^log6 12 = 12
lg 234/lg 9 = (log9 234/log9 10)(log9 10/log9 9)=log9 26*9=log9 26+1
log12 20 -log12 5/6 +log12 6= log12 (20*6)/5 + log12 6=log12 24 + log12 6=log12 144=12