Answer: He qualifies for a special enrollment period and can then enroll in or disenroll from a Part D plan and the subsidy will then apply to the plan he chooses.
Step-by-step explanation:
Medicare Part A helps an individual pay for the hospital and the facility costs such as hospital rooms, meals, nurse care etc.
Medicare Part B helps pay for the medical costs which occurs outside the hospital such as doctor visits etc. Parts A and B are refered to as the Original Medicare and they're run by the federal government.
On the other hand, Part D helps pay for prescription drugs. In this case, since Mr Johannsen gains the Part D low-income subsidy, he qualifies for a special enrollment period and can therefore enroll in or disenroll from a Part D plan and the subsidy will then be applied to the plan he chooses.