Explanation

For a fixed amount of gas, the combined gas law is given by

$$ \frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2} $$

Initial conditions:

$$ P_1 = 2\ \text{atm}, \quad V_1 = 60\ \text{cm}^3, \quad T_1 = 27^\circ\text{C} = 300\ \text{K} $$

Final conditions:

$$ V_2 = 20\ \text{cm}^3, \quad T_2 = 77^\circ\text{C} = 350\ \text{K} $$

Substituting into the equation,

$$ \frac{2 \times 60}{300} = \frac{P_2 \times 20}{350} $$

$$ \frac{120}{300} = \frac{20P_2}{350} $$

$$ \frac{2}{5} = \frac{2P_2}{35} $$

$$ P_2 = 7\ \text{atm} $$

Hence, the final pressure of the gas is

7 atmospheric pressure.

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