Final answer:
The most difficult task in computing the NPV of replacing employees with automated machines in a bagel shop is the estimation of the total change in sales that will result from the change due to uncertainties and external factors.
Step-by-step explanation:
The most difficult task in computing the NPV of replacing employees with automated machines in a bagel shop is the estimation of the total change in sales that will result from the change.
This is because predicting the impact on sales is subject to various uncertainties and external factors that may influence customer behavior.