3(4-2x) - x(7-4) = x over seven minus 2x over 3

3(4-2x) - x(7-4) = x over seven minus 2x over 3

Rewrite as

3(4-2x) - x(3) = x/7 - 2x/3       Simplify

12- 6x - 3x  = x/7 - 2x/3     

12 - 9x=  x/7 - 2x/3      Multiply both sides by the common denominator on the right (21)

252 - 189x = 3x - 14x     Simplify again

252 - 189x = -11x          Add 189x to both sides

252 = 178x                    Divide both sides by 178

252/178 = x = 126/89