Find the Thevenin equivalent.

NOTE: Blue items were added to solve the problem and are not part of the original diagram.

Express current source in terms of mesh currents.

i_a = 8 A

Now, erasing the current source leaves only one mesh (b) around which to write KVL.

12 (i_b - i_a) + 6 i_b - 12 = 0

18 i_b - 12 i_b = 12

18 i_b - 12 (8) = 12

18 i_b = 108

i_b = 6 A

Now, by KVL,

v_oc = v₂ + v₆

v_oc = 2 i_a + 6 i_b

v_oc = 16 + 36 = 52 V

thus

v_Th = 52 V

Next, I will find R_Th by "killing" the independent sources and using resistor combinations.

Hopefully by this point in the course, you can easily see that

R_eq = (12_||6) + 2 = 6 W

Thus

R_Th = 6 W

so the Thevenin equivalent circuit is:

Note that R_Th could also be obtained by finding i_sc then R_Th = v_oc / i_sc.