Sale and leaseback not on market terms

Hi, there is an example in BPP study text p.221 on leaseback (not on market term) which seems to be solved in a different manner than you do in your lecture when it comes to accounting for a lease liability and additional financing . Relying on your example (Ex4 ch. 12 leases) I would resolve the following example from bpp as follows:
Bungle sells a building to Zippy for $800 000. Carrying amt prior to sale was $600 000. Bungle leases the building back for 5 yrs at $120 000 p.a. payable in arrears. Fair value of the building at the date of sale was 750 000, interest rate implicit in the lease is 4,5%. Transaction satisfies performance obligations in IFRS 15.

PV of 120 000 annuity (for 5 yrs at 4,5%) is $526 797. So, I would add the additional financing of $50 000 to this amount (Proceeds less FV = 800 000 – 750 000 = 50 000) – it would give me a $576 797 in total for a lease liability.
Calculation of the Right-of-use asset would be as follows: $600 000 (previous carrying value) x Discounted lease payments ($526 797)/FV ($750 000) = $421 438
So, I would record a gain of $44 641

The whole entry would be:
DR Proceeds $800 000
CR Asset (PPE – building) $600 000
CR Lease liability $576 797
DR Right -of – use $421 437
CR Gain $44 641

However, the bpp provides different explanation. I quote ” 476 797
(526 797 – 50 000) relates to the lease and 50 000 to the additional financing”. The right of use asset is measured in this way : 600 000x 476 797/750 000 = 381 437.
Total gain = 750 000 – 600 000 = 150 000
Gain relating to the rights retained = Gain x dicounted lease pmts/fv = 150 000 x 476 797/750 000=95 360
Gain relating to the rights transferred = 150 000 – 95 360 = 54 640.

BPP’s entry to be recorded is:
DR Proceeds $800 000
CR Asset (PPE – building) $600 000
CR Lease liability $526 797
DR Right -of – use $381 437
CR Gain $54 640

Please advise if I am wrong in my assumption (by adding 50 000 to the PV of lease payments) and in my calculations of Right of use asset and the gain.

Thank you!