Answer:
a) If Bob and Mary replace their old with a new car, which is 15% more expensive, but the car has lots of new functions, like a camera is upgraded to assisting with backing up, has better GPS integration, and better fuel economy. the inflation is heightened, because the price increased and CPI increased too.
b) If Chris uses the same brand of shoes for 15 years, but the price for this shoes have doubled, then this case does not cause inflation to be overstated neither does it cause inflation to be understated.
c) If Donna's favorite chocoholic shrank in size, but the price is still the same, the inflation understated is understated because price price is not affected and CPI stands the same too, but there is inflation.
d) If Zach buys muffins instead of bagels, then the inflation is understated, because according to this switch to another goods, the CPI index will not predict able to predict accurately the change in inflation.