-4c-11=4c+21

2 answers

move similar terms to one side.
-4c=4c+32

then subtract 4c to both sides.
-8c=32

then divide both sides by -8.
c=-4
-4c-11=4c+21

move constants to one side and variables to the other.
add -21 to both sides and add +4c to both sides.
-4c+4c-11-21 = 4c+4c+21-21
-11-21 = 8c
combine terms
-32 = 8c
divide both sides by 8
-32/8 = 8c/8
-4 = c
Check my work. I always check the answer, too, by substituting into the original. In this case we have
(-4*-4) - 11 = (4*-4)+21
+16-11 = -16+21
+5 = +5
GOOD. It checks.