well u move all the variables to the left side, so 8x is already in the left but 7x isnt so you move 7x to the left side of the equal sign which makes 7x to -7x.
8x-2-7x=-9
you move the -2 to the right side of the equal sign which becomes +2.
8x-7x=-9+2
you do the math which 8x-7x=1x and -9+2=-7
so.... 1x=-7
and x=-7. Make sure to always combine like terms.
To make sure it is correct replace the x with the -7 and
8(-7)-2=-9+7(-7)
-56-2=-9-49
-58=-58
so x= -7