Answer:
$2,100
Explanation:
The relevant costs are $2,100.
If the additional costs of $2,100 are incurred then the product 89 could be sold for $9,800.
These incremental costs affect the decision whether to sale the product in $7,000 or incur further costs of $2,100 and as result incremental revenue of $2,100(9,800-7,700) is earned i.e revised selling price less revised cost to produce the product.
Before this further costs incremental revenue was $1,400 (7,000-5,600)