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1.
Select the rectangle whose multiplication you want to find — it turns blue.
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2.
Select a rectangle you already know; it must sit fully inside or completely around the first — it turns green.
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3.
Fill the gap by drawing yellow rectangles. Usually a bottom strip and a right‑hand strip are enough; any shared corner is handled automatically.
Example: to get 6 × 7 from 5 × 5, draw a 1 × 7 strip at the bottom and a 6 × 2 strip on the right — the shared 1 × 2 corner is included automatically.