a) 13a + 2b - 2a - b = (13a - 2a) + (2b - b) = 11a + b
б) 41x - 58x + 6y - y = (41x - 58x) + (6y - y) = -17x + 5y
в) -5,1a - 4b - 4,9a + b = (-5,1a - 4,9a) + (-4b + b) = -10a - 3b
г) 7,5x + y - 8,5x - 3,5y = (7,5x - 8,5x) + (y - 3,5y) = -x - 2,5y