A gaseous reaction occurs at a constant pressure of $40\mathrm{.}0$atm and releases $69\mathrm{.}3kJ$ of heat. Before the reaction, the volume of the system was $8\mathrm{.}80L.$ After the reaction, the volume of the system was $2\mathrm{.}80L.$ Calculate the total internal energy change, $U,$ in kilojoules.

Express your answer with the appropriate units.

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