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

You have a grid of size n x 3 and you want to paint each cell of the grid with exactly one of the three colors: Red, Yellow, or Green while making sure that no two adjacent cells have the same color (i.e., no two cells that share vertical or horizontal sides have the same color).
Given n the number of rows of the grid, return the number of ways you can paint this grid. As the answer may grow large, the answer must be computed modulo 109 + 7.
 
Please complete the following python code precisely:
```python
class Solution:
    def numOfWays(self, n: int) -> int:
```