Answer:
5
Step-by-step explanation:
It is easy: look at the change between m and m - [?]:
3 is 8 - 5
7 is 12 - 5
13 is 18 - 5
15 is 20 - 5
? = 5
For instance,
8 - 5 = 3
12 - 5 = 7
18 - 5 = 13
20 - 5 = 15
Understand?
