Assume question is: -8/(13x)=-12.
Multiply each side by -13x: 8=156x; divide through by 4: 2=39x; divide through by 39: 2/39=x so x=2/39.
If the question is -(8/13)x=-12, then multiply each side by -13: 8x=156; divide each side by 8: x=156/8=39/2=19.5.