ExplanationIf we were just counting all of the squares in the board game we could use multiplication: r rows times r+1 columns.

This would give us

r^2+r squares.

If we take one row out (doesn't matter if its the first, second, third, etc) then we would have r-1 rows times r+1 columns.

If we also then take a column out, we would have r-1 rows times r columns.

So the total number of squares without a column and without a row is

r\times(r−1)=r^2−r.

So option A is correct.
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Sandy

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