(related to Problem: St. George's Banner)
As the flag measures $4$ ft. by $3$ ft., the length of the diagonal (from corner to corner) is $5$ ft. All you need do is to deduct half the length of this diagonal ($2\frac 12$ ft.) from a quarter of the distance all around the edge of the flag ($3\frac 12$ ft.) — a quarter of $14$ ft. The difference ($1$ ft.) is the required width of the arm of the red cross. The area of the cross will then be the same as that of the white ground.
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