Find the difference in temperature between each 1000 feet:
From 1 to 2: 30 - 23.5 = 6.5
From 2 to 3: 23.5 - 17 = 6.5
From 3 to 4: 17 - 10.5 = 6.5
The temperature change is constant as it drops 6.5 degrees for every 1000 foot gain in elevation.
At 5,000 feet the temperature would be : 10.5 - 6.5 = 4
At 6,000 feet: 4 - 6.5 = -2.5
At 7,000 feet: -2.5 - 6.5 = -9
At 8,000 feet: -9 - 6.5 = -15.5
At 8,000 feet the temperature would be -15.5 degrees.
