Answer:
1 company to be in different is  15000 units
2 cost =  approximate  $300000
3 Total annual costs  = approximate $380,000
4  cost is less for phoenix and  Phoenix is the ideal location
5 Cost advantage = $18,000 so closed to $20000 
Explanation:
given data 
Atlanta fixed costs (annual) = 80000
variable costs (per unit) = 20 
Phoenix  fixed costs = 140000 
variable costs = 16
solution
we consider here output level = x 
and price will be = p
so here profit for location will be 
profit = Revenue - Variable Cost - Fixed costs   .............1
so here Atlanta profit is  
Profit = px - 20x - 80000     ..................2
and Phoenix profit is  
Profit = px - 16.1x - 140,000      ...................3
so now company to be in different is  
px - 20x - 80000 = px - 16.1x - 140,000
solve we get x here 
x =  15,384.62  = 15000 units 
and  
and now annual costs for phoenix will be as 
annual cost =  Variable cost + Fixed     ...........4
cost = 16.1 × 10,000 + 140,000
cost = 161,000 + 140,000
cost = $301,000 = approximate  $300000
and 
Total annual costs will be as 
Total annual costs = 20 × 15,384.62 + 80,000
Total annual costs = $387,692.3 = approximate $380,000   
and 
Annual demand = 20,000 units
so  
Cost for Atlanta  = 20 × 20000 + 80,000 
Cost for Atlanta  = $480,000
Cost for Phoenix = 16.1 × 20000 + 140,000
Cost for Phoenix = $462,000
so 
cost is less for phoenix and  Phoenix is the ideal location
and
now Cost advantage will be
Cost advantage  = $480,000 - 462,000
Cost advantage = $18,000 so closed to $20000