First, add #6# to both sides. Then, multiply by #3# and also #-1#. Here's what that looks like:
# -1/3x-6=3 #
# -1/3x-6color(blue)+color(blue)6=3color(blue)+color(blue)6 #
# -1/3xcolor(red)cancelcolor(black)(color(black)-6color(blue)+color(blue)6)=3color(blue)+color(blue)6 #
# -1/3x=3color(blue)+color(blue)6 #
# -1/3x=9 #
# -1/3xcolor(blue)(*3)=9color(blue)(*3) #
# -1/color(red)cancelcolor(black)3xcolor(blue)*color(red)cancelcolor(blue)3=9color(blue)(*3) #
# -x=9color(blue)(*3) #
# -x=27 #
# -xcolor(blue)(\*-1)=27color(blue)(*-1) #
# color(red)cancelcolor(black)-xcolor(blue)(\*color(red)cancelcolor(blue)-1)=27color(blue)(*-1) #
# x=27color(blue)(*-1) #
# x=-27 #
That's the answer. Hope this helped!