Question 841718
Do you mean this : {{{(12 + 8sqrt(81))/(-6)}}}? 
If you mean so, the first thing you have to do is find out what is {{{sqrt(81)}}}
{{{sqrt(81) = 9}}}
Then the problem will become 
{{{(12 + 8*9)/(-6)}}}
{{{(12 + 72)/(-6)}}}
{{{84/(-6)}}}
{{{-14}}}
TA-DAH 
:D