Current through $20\, \Omega$ resistor $i=\frac{12}{40}$

Charge on the capacitor at steady state.

$q_{0}=25 \times \frac{12}{40} \times 20=150\, \mu C$

at $t=0,$ $S$ witch is opened, $i = {i_0}{e^{ - t/\tau }}$

$\tau=\mathrm{RC}=20 \times 25=500\, \mu \mathrm{S}$

Current $\quad {\rm{i}} = \frac{{{{\rm{q}}_0}}}{\tau }{{\rm{e}}^{\frac{{0.25 + {{10}^{ - 3}}}}{{500 \times {{10}^{ - 6}}}}}}$

$\mathrm{i}=\frac{150}{500} \mathrm{e}^{-1 / 2}=0.189 \mathrm{\,A}$