chapter lease

hi
i would appreciate if someone can help me pls

Question
explain how the seller accounts for the sale and lease back transaction.

1. sale at undervalue and operating lease back

sale value- 10,000
fair value- 15,000
carrying value- 12,000

my answer is-

Dr Bank 10,000
Dr Prepayment 5,000
Cr Disposal a\c (income statement) 15,000

Dr Disposal a\c 12,000
Cr NCA 12,000

this means profit on disposal is 3000.
i assumed that a prepayment was made towards the operating lease.
however my answer is not correct.

it should have been

Dr bank 10,000
Cr disposal 10,000

Dr Disposal 12,000
Cr NCA 12,000

Loss on disposal 2,000

can someone please explain how they got the answer? i guess they got the answer by assuming that the company needed cash immediately so it sold it for a lower value..but this is just an assumption, my calculation above also was based on the assumption that a prepayment was made for the leased asset.
i really need help
thank you

thanks a lot