Answer:
To make it feasible it will need to operate 7 or more planes.
Explanation:
450,000 maintenance facility
useful life of 15 year
salvage value of 100,000
<u>saving cost per plane:</u>
third party cost - own facility cost = cost savings
            35,000  -          25,000      =    10,000
present value of the salvage value: (present value of a lump sum)
  
  
 salvage $ 100,000
 time  15 years
Minimum accepter rate of return: 0.12000
  
  
 PV   18,269.6261 
present worth of the facility:
450,000- 18,268.63 = 431,731.37
Now we determinate the PMT over a 15 years period to know the cost savings per year to justify the facility:
 
 
PV	431,731
time	15
rate	0.12
 
 
C  $ 63,388.630 
As each plane cost savings are 10,000
63,388.62  / 10,000 = 6.39
the company will need to operate 7 or more planes.