If three moles of an ideal gas at \( 300 \, \text{K} \) expand isothermally from \( 30 \, \text{dm}^3 \) to \( 45 \, \text{dm}^3 \) against a constant opposing pressure of \( 80 \, \text{kPa} \), then the amount of heat transferred is __________ \( \text{J} \).
