The correct answer is 45.

Solution:

Considering the given number pattern.

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

Note that:
30 + 5 = 35
35 + 5 = 40
40 + 5 = 45
45 + 5 = 50

So, the rule is "add 5".

Then, the missing number is 45.