First, remove all of the terms from parenthesis. Be careful to handle the signs of each individual term correctly:
#sqrt(12) - 4 - 8 - sqrt(27)#
Next, group like terms:
#sqrt(12) - sqrt(27) - 4 - 8#
Then, combine like terms:
#sqrt(12) - sqrt(27) - 12#
Now, use this rule of radicals to simplify and combine the radicals:
#sqrt(color(red)(a) * color(blue)(b)) = sqrt(color(red)(a)) * sqrt(color(blue)(b))#
#sqrt(color(red)(4) * color(blue)(3)) - sqrt(color(red)(9) * color(blue)(3)) - 12#
#sqrt(color(red)(4))sqrt(color(blue)(3)) - sqrt(color(red)(9))sqrt(color(blue)(3)) - 12#
#2sqrt(color(blue)(3)) - 3sqrt(color(blue)(3)) - 12#
#(2 - 3)sqrt(color(blue)(3)) - 12#
#-1sqrt(color(blue)(3)) - 12#
#-sqrt(color(blue)(3)) - 12#
Or
#-12 - sqrt(color(blue)(3))#