Using Table A-20, calculate the change of internal energy of 10kg of air modeled as the ideal gas in a closed system when the air temperature decreases from 800K to 500K and assuming specific heats to be constant in this range. 1. calculate the average value of the relevant specific heat in the given range of temepratures in the same units as in the table, 2. calculate the change of internal energy Enter the answer in kJ with the right sign. Do not round the answer.