Math Help - congruence [I have no idea how to solve this]

1. congruence [I have no idea how to solve this]

any explanation??
Thank you so much

2. solution

$[4]_{2} = {...,0,2,4,6,8,...}$

$[4]_{3} = {...,-2,1,4,7,10,...}$

$[4]_{6} = {...,-8,-2,4,10,16,...}$

$[4]_{8} = {...,-12,-4,4,12,20,...}$

is this True?