Find all solutions $x,$ if they exist, to the linear congruences. If solution does not exist, prove the same.

$3+3+4+4=14$

$($a$)3x-=4(mod7)$

$($b$)5x-=-5(mod12)$

$($c$)4x-=12(mod8)$

$($d$)4x-=11(mod8)$