Reducir los siguientes polinomios: 7a - 9b +6a - 4b = a + b – c – b – c + 2c – a = 5x – 11y – 9 + 20x – 1 – y = – 6m + 8n +5 – m – n – 6m – 11 = –a + b + 2b – 2c + 3a + 2c – 3b = – 81x + 19y – 30z + 6y + 80x + x – 25y 15a2 - 6ab - 8a2 +20 –5ab –31 + a2 -ab = –3a +4b – 6a + 81b –114b + 31a –a –b =