The plus sign means that we have to sum all the terms inside of the second parenthesis, while the minus sign means that we have to change all the signs inside the last parenthesis:
[tex](3x+5)+(2x-9)-(4x+3)=3x+5+2x-9-4x-3[/tex]
Now we only have to gather all like terms:
[tex]3x+2x-4x+5-9-3 = (3+2-4)x+(5-9-3)=x-7[/tex]
