Final answer:
The average rate of change of T concerning over the interval from 21,000 to 31,000 ft is calculated as the difference in T values divided by the altitude change, but specific values for T1 and T2 at those altitudes are required to give a numerical result.
Step-by-step explanation:
This is done by finding the slope of the line connecting the points that represent the given interval values. By using the rise over run formula, you can calculate the average rate of change. Unfortunately, the provided information does not include relevant data for altitudes from 21,000 ft to 31,000 ft directly, so we cannot compute the answer precisely from the given data. However, if we had a similar table as the 'Altitude to Air Density Relationship' provided, that covers the given interval, we would subtract the value of T at 21,000 ft from the value of T at 31,000 ft (rise), and then divide by the difference in altitude (run, which is 31,000 - 21,000 ft). For example, if the T values were T1 at 21,000 ft and T2 at 31,000 ft, the average rate of change would be calculated as: (T2 - T1)/(31,000 ft - 21,000 ft).