a) 

Wiemy, że:

$120+45=165$

A więc:

$45+\boxed{120}=165$

$165-\boxed{45}=120$

$\boxed{165}-120=45$

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b) 

Wiemy, że:

$369-35=334$

A więc:

$369-\boxed{334}=35$

$334+\boxed{35}=369$

$\boxed{35}+334=369$

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c)

Wiemy, że:

$873-61=812$

A więc:

$\boxed{873}-\boxed{812}=61$

$\boxed{812}+\boxed{61}=873$

$61+\boxed{812}=873$