-2x-6=8(mod4)
-2x-6 + 2*4 = 8+ 2*4 (mod 4)
-2x + 2 = 16 (mod 4)
-2x + 2 = 0 (mod 4)
2x = 2 (mod 4)
x= 1 (mod 2) и 2x=6(mod4)⇔x=3(mod4)