Final answer:
Heather's gross income is reduced by $800, the reimbursed amount for her medical expenses under the company's flexible spending plan, and she will not get the unused $400 back.
Step-by-step explanation:
The situation described with Heather involves a flexible spending plan, which is a specialized account used to pay for specific medical expenses with pre-tax dollars, thus reducing her taxable income. Since Heather elected to reduce her salary by $1,200 to contribute to the plan but only received $800 in reimbursement for her medical expenses, she will not receive the remaining $400 back as it is often a 'use-it-or-lose-it' type of benefit.
Consequently, the proper amount by which Heather's gross income is reduced is the amount of the qualified expenses for which she received reimbursement, which is $800. Therefore, her gross income will be reduced by $800, not by the full $1,200 she contributed to the flexible spending account.