no 2 a-b tolong di bantu sya gak ngerti

2.a)
(13a - 8b) + (21a + 9b) = 13a + 21a - 8b + 9b
                                     = 34a + b

2.b)
(15i - 14j + 13k) + (-30i - 45j + 51k) = 15i - 30i - 14j - 45j + 13k + 51k
                                                         = -15i - 59j + 64k