80. 1) 43x + 72 = 502; 2) 67 − 21y = 25; 3) 19y − 200 = 47; 4) 83 + 29x = 982.

1. \(43x+72=502\)
   \(43x=502-72=430\)
   \(x=430:43=10\).
2. \(67-21y=25\)
   \(21y=67-25=42\)
   \(y=42:21=2\).
3. \(19y-200=47\)
   \(19y=47+200=247\)
   \(y=247:19=13\).
4. \(83+29x=982\)
   \(29x=982-83=899\)
   \(x=899:29=31\).

Ответ: 1) x = 10; 2) y = 2; 3) y = 13; 4) x = 31.