ECON 1102 – Should a firm shut down (and why) if its revenue is $1,000 per week

Question
1. Should a firm shut down (and why) if its revenue is $1,000 per week, and:

a) its variable cost is $500, and its sunk fixed cost is $600?

b) its variable cost is $1,001, and its sunk fixed cost is $500?

2. Should a firm shut down if its weekly revenue is $1,000, its variable cost is $500, and its fixed cost is $800, of which $600 is avoidable if it shuts down? Why?