Ответ:

  1. \((39+x)-84=78\)
    \(39+x=162\)
    \(x=123\)
  2. \((x-83)+316=425\)
    \(x-83=109\)
    \(x=192\)
  3. \((600-x)-92=126\)
    \(600-x=218\)
    \(x=382\)
  4. \(253-(x-459)=138\)
    \(x-459=115\)
    \(x=574\)
  5. \(502-(217-x)=421\)
    \(217-x=81\)
    \(x=136\)
  6. \(871-(x+157)=385\)
    \(x+157=486\)
    \(x=329\)

Ответ: 1) x = 123; 2) x = 192; 3) x = 382; 4) x = 574; 5) x = 136; 6) x = 329.