\displaystyle V_x = 6 \times 3 = 18(\mathrm{V})

\displaystyle V_{\mathrm{oc}} = 12 + 3 \times (6 + 3) + 2V_x= 65(\mathrm{V})

\displaystyle i_2 - i_1 = 3,\quad 12 - 9i_1 + (-12i_1) = 0

\displaystyle i_1 = \frac{4}{7}(\mathrm{A}),\quad i_2 = \frac{25}{7}(\mathrm{A}) = I_{\mathrm{sc}}

\displaystyle R_{\mathrm{Th}} = \frac{V_{\mathrm{oc}}}{I_{\mathrm{sc}}}= \frac{91}{5}(\Omega) = R_L

\displaystyle P_L = \frac{V_{\mathrm{oc}}^2}{4R_L}= \frac{65^2}{4 \times 91}= \frac{1625}{28}(\mathrm{W}),\quad p + q = 1653