in equations you must do the same to both sides so that the equation stays equal. also, it's easier to solve if you get the unknowns on one side.
so first you distribute
-7(x-4) means (-7 times x) + (-7 times -4) so -7x+28
-7x+28+8x=12+14
add like terms
x+28=26
subtract 28 from both sides
x=-2