Answer:
18
Step-by-step explanation:
Let's call the first number n. The next four numbers will be n + 3, n + 6, n + 9 and n + 12. Then, we have
n + n + 3 + n + 6 + n + 9 + n + 12 = 105
5n + 30 = 105
5n = 75
n = 15
The second smallest number is n + 3 which is 15 + 3 = 18.
