impairment

Hi, i am doing impairment question in BPP rev kit and cannot undertsand pro rota Question ask cash generating unit comprises the following Assets: $000 Building 700 Plant and equipment 200 Good Will 90 Current Assets 20 Total 1,010 one of the machine carried at $40,000, is damaged and will have to scrapped.The recoverable amount of the cash generating unit is at $750,000 What will be the carrying amount of the building when the impairment loss has been recognised. i do understand the imapairment loss recognisedis $130,000 but dont understand how that pro rota into building and plant. please help to pro rota that: many thanks