How to use voltage division for series-parallel circuit
G36 is correct. I'll try to provide a little explanation to what he's saying.

Since the 12 ohm and 6 ohm resistors are in parallel, the voltage across both of them is the same \$V_x\$ Volts. So you can find out the equivalent resistance as \$R_{eq} = 12||6 = \frac{12*6}{12+6} = 4\$. So now, you have a 4 ohm resistor in series with a 8 ohm resistor. Using voltage division, you get \$V_x = V_c * \frac{4}{4+8} = \frac{V_c}{3}\$.