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

You are given an integer array nums consisting of n elements, and an integer k.
Find a contiguous subarray whose length is equal to k that has the maximum average value and return this value. Any answer with a calculation error less than 10-5 will be accepted.
 
Please complete the following python code precisely:
```python
class Solution:
    def findMaxAverage(self, nums: List[int], k: int) -> float:
```