The correct answer is 15.

Solution:

Considering the given number pattern.

Here, the numbers are decreasing.
So, to find the missing number, we first find the rule.

Note that:
30 - 5 = 25
25 - 5 = 20
20 - 5 = 15
15 - 5 = 10

So, the rule is "subtract 5".

Then, the missing number is 15.