\textbf{161-} An ideal gas with volume 2 liters at constant pressure $P = 10^5\,\text{Pa}$ gives heat to the surroundings and its volume becomes $1.5$ liters. How many joules of work is done on the gas?
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(1) $-50$ \hspace{1cm} (2) $-30$ \hspace{1cm} (3) $30$ \hspace{1cm} (4) $50$
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