Query re Treatment of Deferred Tax Liability Post Acq Movement

Hello,
My query concerns a question in the BPP SBR Practice & Revision Kit (Question 14 Bravado)

A Deferred Tax liability is accounted for on acquisition of Mixted, because the Tax Written Down Value of Mixted Net Assets, is less than their Net Book Value at the date of acquisition. This is understood.
However, per the BPP answer, it appears that the deferred tax liability balance is “written off” over 7 years, being the remaining useful economic life, at the date of acquisition of PPE of Mixted, which was subject to a fair value uplift at acquisition date. The deferred tax liability balance of 3 is written off for 0.4 (3/7 years), with the 0.4 being debited against deferred tax liability, Cr Group Retained Egs 0.3 (0.4*70%) and Cr NCI 0.1 (0.4 * 30%).

I am confused as to the subsequent “write off” of the deferred tax liability balance?? Any guidance you could provide would be much appreciated

Thanks
Liam