Step 1: Use the combined gas law.
For a fixed amount of ideal gas,
\[
\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}
\]
Step 2: Write the given values.
Initial pressure:
\[
P_1=12\,\text{atm}
\]
Initial volume:
\[
V_1=10\,\text{L}
\]
Initial temperature:
\[
T_1=27^\circ\text{C}=300\,\text{K}
\]
Final volume:
\[
V_2=6\,\text{L}
\]
Temperature is increased by \(30^\circ\text{C}\), so
\[
T_2=57^\circ\text{C}=330\,\text{K}
\]
Step 3: Substitute in the formula.
\[
\frac{12\times 10}{300}=\frac{P_2\times 6}{330}
\]
So,
\[
P_2=\frac{12\times 10\times 330}{300\times 6}
\]
\[
P_2=22\,\text{atm}
\]
Step 4: Final conclusion.
Hence, the final pressure of the gas is
\[
\boxed{22\,\text{atm}}
\]