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Given, 0.5x + 0.9y = 8.1
or, 5x +9y= 81; it is linear Diophantine equation.
So, either, x = 0 and y =9
or, x = 9 and y =4, so, x+y = 13.

So, I think C. :)
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Low-resolution image: Multiple of 5

High-resolution image: Multiple of 9


\(\frac{81 }{ 9} = 9\) high resolution images. But low-resolution images cannot be zero.

Reduce multiples of 9 in such a way that the difference of 81 - multiple of 9 is multiple of 5.


=> 81 - 36 = 45

Hence, 4 * 9 = 36 [4 high resolution images] and 5 * 9 = 45[9 high resolution images]

Total images: 4 + 9 = 13

Answer C
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