Notice that the rate of change is constant.
Part A.
As stated in the question, the first ordered pair is (0,6) because at time x=0, the height of the candle is equal to its original height (6 in).
Therefore, after an hour (x=1), its height has been reduced by 0.5in; then, the corresponding ordered pair is (1,6-0.5)=(1,5.5).
Similarly, as for the remaining ordered pairs,
Each time x increases by 1, y decreases by 0.5.