Ответ:
Упростим выражения:
15a ⋅ 4 = 15 ⋅ 4 ⋅ a = 60a
3b ⋅ 12 = 3 ⋅ 12 ⋅ b = 36b
17a ⋅ 5 = 17 ⋅ 5 ⋅ a = 85a
11a ⋅ 7 = 11 ⋅ 7 ⋅ a = 77a
21d - 18d + 3 = (21 - 18)d + 3 = 3d + 3
14a + a + 9 + 4 = (14 + 1)a + (9 + 4) = 15a + 13