chapter 25 ex 2 Group SFP incl. Associate

Hi.
kindly if you could help me with the following adj

On 1 January 2019, Hartsop acquired 70% of the equity interest of Skiddaw for a cash consideration of $1,340 million. At 1 January 2014, the identifiable net assets of Skiddaw had a fair value of $1,850 million, and retained earnings were $450 million. The excess in fair value is due to an item of property, plant and equipment that has a remaining useful life of 10 years.

i understood that PPE at fair value would be valued at $400 but cannot understand how depn figure amount to $80.

please help!thanks