I guess the question is to solve the equation
4x - 7 - ( x + 4 ) = 3x + 4 - ( 2x - 1 )
we know that,
- ( a + b ) = -a - b
so ,
4x - 7 -x - 4 = 3x + 4 - ( 2x - 1 )
we have,
-( a -b ) = -a + b
so,
4x - 7 - x - 4 = 3x + 4 -2x + 1
4x - x -7 -4 = 3x -2x + 4 + 1
3x - 11 = x + 5
taking all the x terms on LHS and all the constants on RHS,
3x - x = 5 + 11
2x = 16
x = 8