IF AN ECONOMY MOVES FROM PRODUCING 15 UNITS OF A AND 7 UNITS OF B TO PRODUCING 10 AS AND 8BS, THE OPPORTUNITY COST OF THE 8TH B IS:

1 10AS
2 5AS
3 7AS

To calculate the opportunity cost, we need to determine the trade-off or sacrifice involved in the decision. In this case, we are comparing the production of A and B before and after the change in production.

The opportunity cost of the 8th B is the amount of A that needs to be sacrificed to produce an additional unit of B.

Before the change in production:
- 15 units of A and 7 units of B were produced.

After the change in production:
- 10 units of A and 8 units of B are produced.

To find the opportunity cost of the 8th B, we need to calculate the difference in the amount of A produced before and after the change.

Before the change, 15 units of A were produced and after the change, 10 units of A are produced.

So, the opportunity cost of the 8th B is 15 - 10 = 5 units of A.

Therefore, the answer is: 2) 5 AS.