4 Player Board Game

Four players are playing a game involving choosing $$1\times1$$ squares on a grid of size $$3 \times 8$$. Each player chooses a random square on the grid, then all players reveal their choices and a token is placed in the center of each of these squares. The probability that the tokens form the vertices of a non-degenerate rectangle can be expressed as $$\frac{a}{b}$$ where $$a$$ and $$b$$ are coprime positive integers. What is the value of $$a + b?$$

Details and assumptions

Players are allowed to have selected the same squares. There is no restriction on their choices.
A degenerate rectangle has 0 area.
Squares are rectangles.

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