disposal of copyright

31 March 2021, Jessica sold a copyright for £28,800. The copyright had been purchased on 1 April 2015 for £21,000 when it had an unexpired life of 15 years. What is Jessica’s chargeable gain in respect of the disposal of the copyright A £0 B £20,400 C £16,200 D £7,800 the solution in the text ale proceeds 28,800 Less: Allowable element of acquisition cost (W) (12,600) ––––––– Chargeable gain 16,200 ––––––– Working: Allowable element of acquisition cost Remaining life at disposal = 9 years Estimated useful life = 15 years Allowable cost = £21,000 × 9/15 = £12,600 Hello Sir may you please help me understand why they used the remaining years 9 instead of the period of ownership 6