Step 1: Apply the combined gas law.
The combined gas law is given by:
\[
\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}.
\]
Substitute the given values for the initial and final states:
\[
\frac{1 \, \text{atm} \times 60 \, \text{mL}}{27°C + 273} = \frac{P \times 30 \, \text{mL}}{77°C + 273}.
\]
\[
\frac{1 \times 60}{300} = \frac{P \times 30}{350}.
\]
Step 2: Solve for \( P \).
Cross-multiply to find \( P \):
\[
P = \frac{60 \times 350}{300 \times 30} = \frac{7}{3} \, \text{atm}.
\]
Final Answer:
\[
\boxed{\frac{7}{3} \, \text{atm}}.
\]