x/4+x/(x-4)=4/(x-4)

x/4+x/(x-4)=4/(x-4)     subtract  x/(x -4) from both sides

x/4  = 4/(x-4) -  x / (x - 4)

x/4 = (4 - x) / (x -4)    factor out a negative in the numerator on the right

x/4 = -(x - 4)/ (x -4)          [note....   -a/a  = -1]

x/4 = -1      multiply both sides by 4

x = -4