CGUs

Good evening,

I have a small issue with the impairment of a CGUs, and I am kindly asking for your help.
I came across the following exercise:

” A company runs a unit that suffers a massive drop in income due to failure of its technology on 1 January 20X8. The following carrying values were recorded in the books immediately prior to the impairment:

Goodwill $20 m
Technology $ 5 m
Brands $10 m
Land $50 m
Buildings $30 m
Other net assets $40 m

The recoverable value of the unit is estimated at $85 million. The technology is worthless. It is considered that the book value of other net assets is a reasonable representation of its NRV.
Show the impact of the impairment on 1 January.”

I understood that the CV is $155 million and the recoverable amount $85 million thus, resulting in an impairment of $70 million, from which we have to deduct $5 million, attributable to technology. So the impairment expense is $65 million.

However, I am confused when it comes to the pro-rata basis. In the book, after deducting Goodwill from the total impairment, they take into account only the CVs of Brands, Land and Buildings excluding the Other net assets. And my question is why? I do not fully understand the process.

Thank you!