\textbf{168.} The temperature of 2 moles of an ideal gas increases from $30°C$ to $80°C$ at constant pressure. How many joules of work is done on the gas in this process?
\[
\left(R = 8.3\ \frac{\text{J}}{\text{mol.K}}\right)
\]
\[
(1)\ 415 \qquad (2)\ -415 \qquad (3)\ 830 \qquad (4)\ -830
\]