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Explanation:
Let's say the original photo is 2 inches by 2 inches. The area here is 2*2 = 4.
Now lets scale up each dimension by a factor of 6. The new larger photo is now 12 inches by 12 inches (since 2*6 = 12). The new area is 12*12 = 144.
Dividing the two areas leads to 144/4 = 36 showing the new photo has 36 times more area compared to the old one.
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Here is a more general proof.
The old photo is x inches by y inches. The old area is xy.
The new photo is 6x inches by 6y inches.
We see that,
new area = 6x*6y = 6*6xy = 36xy = 36*(old area)