Answer: 15,000 units
Step-by-step explanation:
The annual output that would make them indifferent is the one that would equate both costs.
Assume that output is x.
80,000 + 20x = 140,000 + 16x
20x - 16x = 140,000 - 80,000
4x = 60,000
x = 60,000/4
x = 15,000 units