Add: 3+2y−5y2+6y3, −8+3y+7y3 and 5−6y−8y3+y2
(3+2y−5y2+6y3) + (−8+3y+7y3) + (5−6y−8y3+y2)
= (6y3+7y3−8y3) + (−5y2+y2) + (2y+3y−6y) + (3−8+5)
= 5y3−4y2−y
Adding 3+2y−5y2+6y3,−8+3y+7y3 and 5−6y−8y3+y2, we get