We have 2 coins placed in one cell of a 6 by 6 grid.
We have to calculate the probability of the two coins not being in the same row or column.
We can think of this as a two-step problem.
The first coin can be in any cell and it won't affect the probability of the two coins being in the same row or column.
Then, once the first coin is placed in a cell, the places where the second coin can be without being in the same row or column of the first coin are limited.
We can see it in a drawing as:
We can then see that the original grid has 6*6 = 36 cells.
If one is occupied by the first coin, 35 cells are left for the secoind coin.
As the coin can not be in the same row or column is like we take one row and one column of the grid: the second coin has 5*5 = 25 cells to be placed without breaking the rule.
Then, if all cells have the same probability for the second coin, there is a probability of 25/35 = 5/7 (approximately 0.71) for the second coin to not be in the same row or column than the first coin.