Answer: $720000
Explanation:
Sunk cos simply refers to a coat which a company has already incurred and can't be recovered. They're not relevant to future decisions if the company has they already happened in the past.
In this case, the sink cost will be $720,000 which is the total cost of the obsolete microcomputers, Other coat such as $100,000, $160,000, and $50,000 are relevant cost.