Answer:
b. $2 billion trade surplus with country B.
Step-by-step explanation:
When a country exports more than it imports, it is said that the country has a trade surplus. On the other hand, when a country imports more than it exports, it is said that the country has a trade deficit.
In this case, exports to country B are worth $10 billion which are larger than the $8 billion of imports from country B. Country A's trade surplus is given by:

Therefore, the answer is alternative b.