Coolit Company installed a new air conditioning system in their main office on January 1, 2008. The system cost $300,000 and was expected to last 10 years (no Salvage Value). On March 31, 2009, new fluorocarbon emission guidelines led to the replacement of the principal cooling mechanism at a cost of $105,000. The life of the cooling system nor its salvage value was affected bu the efficiency was greatly increased. Coolit uses the straight-line method of depreciation. The depreciation expense for the year 2009 was:

a) $30,000
b) $37,000
c) $39,000
d) $40,000

I forgot to explain what I'm having trouble with for this particular problem. I understand what the straight-line method is and how to find the depreciation expense for a partial year. Is the new cost of the system on March 31, 2009 $405,000? (if the system was replaced for a cost of 105,000, I am assuming the company exchanged the system that cost 300,000 for the new system and paid the difference with 105,000). Would you find the depreciation expense for the first 3 months of 2009 at the original cost, and the depreciation expense for the rest of the year with the new cost?