How Do I Get The Answer For -3(x+4)=7(2x-5) ?

Multiply out both sides; then combine terms. After the first step, you get

-3x -12 = 14 x -35
Add 3x and 35 to both sides, to get only an "x" term on one side of the equation and only a constant on the other
17 x = 23
Now divide both sides by 17.
x = 23/17