Work Step by Step
We first cancel out the -9c by adding 9c to both sides to get that $-21c-6=-3$. We need to get the c alone. Thus, we cancel out the subtraction by adding 6 on both sides. This leaves us with the equation $-21c=3$. In order to cancel out multiplication, we use division, so we divide both sides by $-21$ to get that $c=-1/7$.