P $7\mathrm{.}8-4$ The switch in the circuit shown in Figure P $7\mathrm{.}8-4$ has been closed for along time before itopens attime $t=0.$ Determine the values of $v_R(0-)$ and $v_L(0-),$ the voltage across the $4-$ resistor and the inductor immediately before the switch opens, and the values of $v_R(0+)$ and $v_L(0+),$ the voltage across the $4-$ resistor and the inductor immediately after the switch opens.