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There is a picture. Find out what number is needed to replace this question mark.

enter image description here

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5
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The answer is

41

because

Each number in the third row is the difference of the product and sum of the numbers in the same column of the first and second rows.
i.e. $C = A\times B -(A+B)$

$5\times7 - (5+7) = 35 - 12 = 23$
$12\times9 - (12+9) = 108 - 21 = 87$

$15\times4 - (15+4) = 60 - 19 = 41$

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1
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I found the same answer as @Apep's, but in a different way a different answer.

$?=17$

For some $x$, let $|x|=\sqrt{x^2}$. This is the notation I will be using for the following pattern.

The first column has $5$, $7$ and lastly $|23|$. $$23+1\times |5-7|=5^2\tag{$\times 1$ since it is the $1^\text{st}$ column}$$ $5$ is the lowest out of $5$ and $7$.

The second column has $12$, $9$ and lastly $|87|$. $$87-2\times |12-9|=9^2\tag{$\times 2$ since it is the $2^\text{nd}$ column}$$ $9$ is the lowest out of $12$ and $9$.

Note that since this column has a minus instead of a plus, then the overall pattern is therefore going to have alternating signs, implying that the following column will have a plus sign.

Therefore:

In the third column, if we let the question mark be $\rm A$ for Answer, then it is going to look like this: $$\rm{A}+3\times|15-4|=4^2$$ Since $\rm A = -17$, then in the last number of the third column, the answer is going to be $|$$-17|$ which is $17$.

Having the inclusion of $|\cdot |$ allows there to be no negative numbers.

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