\( 75 \, cm^3 \) of propane was completely combusted in \( 400 \, cm^3 \) of oxygen according to the following equation: \( CH_3CH_2CH_3(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(l) \). What is the volume of unreacted oxygen remaining at the original conditions?