i'll do it step-by-step here. if there's any step that doesn't make sense, feel free to let me know!
6c = 2(3c-4) + 2c
distribute the 2 among the terms in the parentheses first.
6c = 6c - 8 + 2c
because both sides have 6c, we can cancel them out. 6c - 6c = 0.
0 = -8 + 2c
move the 8 to the other side (+8 to both sides).
8 = 2c
divide both sides by 2.
8/2 = c
therefore, 4 = c.
hope i helped! good luck.