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Answer: $3$

Substitution

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  So 2

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   are worth 2 more than 2

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3

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  would be worth 2 less ie. 9, so each 

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  is worth 3.

Elimination

Consider the third column:

$2$

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 $+$ 

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 $=13$            $(1)$

and the second row:

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  $+ 2$ 

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  $=11$          $(2)$

$2 \times (2) - (1)$ yields:

$3$ 

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 $=9$

So 

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$=3$.