The sum of two positive integers is 80 and the difference

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The sum of two positive integers is 80 and the difference between them is 20. What is the difference between squares of those numbers ?

Let the numbers be x and y where x > y.
∴ x + y = 80
x – y = 20
∴ (x + y) (x – y) = 80 × 20
⇒ x² – y² = 1600