Answer:
$9120
Explanation:
Using sum of years digit,
5+4+3+2+1=15
5/15*(72000-3600)=22800 for first year
4/15*68400 = 18240 for second year
Total depreciation before change of accounting policy = 22800+18240=41040
Net value of asset at start of 2018 = 68400-41040= 27360
Straight line depreciation for 2018 = 27360/3 = 9120