Two squares chosen on a board: probability they share (or do not share) a side

This type of question, asked 2 times: 2021 Paper 24, 23 Jan 2025. All 2 questions below, oldest first.

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Question 1
2021 Paper 24
66 $Two squares are chosen at random on a chessboard (see figure). The probability that they have a side in common is:$
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Question 2
23 Jan 2025
135 $A board has 16 squares as shown in the figure : Out of these 16 squares, two squares are chosen at random. The probability that they have no side in common is :$
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