First we resolve the part between the square brackets:
[tex]\lbrack x-(7+x)\rbrack=(x-7-x)=0x-7=-7[/tex]Then:
[tex]9-\lbrack x-(7+x)\rbrack=9-(-7)[/tex]Then you apply the opperation with the symbols knowin that:
[tex](+)(+)=+[/tex][tex](+)(-)=-[/tex][tex](-)(-)=+[/tex]And the final answer is:
[tex]9+7=16[/tex]