BPP Quodos Question Pg 128 – Capital allowances

Quodos started to trade on 1 July 2015, preparing accounts to 31 December 2015 and each 31 December
thereafter. On 1 August 2015 he bought a car for £17,000 with CO2 emissions of 110 g/km. The private use
proportion is 10%. The car was sold in July 2018 for £4,000. Quodos has no other assets which qualify for
capital allowances.
Calculate the capital allowances, assuming:
(a) The car was used by an employee, or
(b) The car was used by Quodos
and that the capital allowances rates in 2015/16 apply throughout.

for part (a) they took the balance to the next period as tax WDV c/f but for part (b) they calculated balancing allowance. I understand balancing allowance only arises if the business ceases trade. I do not understand why they calculated the balance allowance for part b.