Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.
 
Please complete the following python code precisely:
```python
class Solution:
    def numOfSubarrays(self, arr: List[int], k: int, threshold: int) -> int:
```