Final answer:
The unused capacity in terms of the number of orders processed is 8,000 orders.
Step-by-step explanation:
To determine the unused capacity in terms of the number of orders processed, we need to calculate the total capacity of the engineers and subtract it from the total number of orders processed. We know that each engineer can process 12,000 orders in a year and there are 9 engineers. So the total capacity is 9 x 12,000 = 108,000 orders.
Since last year 100,000 orders were processed, the unused capacity is 108,000 - 100,000 = 8,000 orders.
Therefore, the unused capacity in terms of the number of orders processed is 8,000 orders (option b).