Answer:
$15
Step-by-step explanation:
The computation of the average fixed cost is shown below:
As we know that 
Average fixed cost is 
= Total fixed cost ÷ Quantity
where, 
Total fixed cost is 
= Total cost - total variable cost 
= $1,200 - $200 × 3
= $1,200 - $600
= $600
And the quantity is 40 products
So, the average fixed cost is 
= $600 ÷ 40
= $15