Final answer:
The unit cost of a box of 20 trash bags is $0.17 per trash bag.
Step-by-step explanation:
The unit cost is calculated by dividing the total cost by the number of units. In this case, the total cost is $3.40 and the number of units is 20 trash bags. To find the unit cost, we divide $3.40 by 20:
Unit cost = Total cost / Number of units
Unit cost = $3.40 / 20
Unit cost = $0.17 per trash bag.