roll over relief

dear tutor:
132 Alice is in business as a sole trader. On 13 May 2021,she sold a freehold warehouse for£184,000, and this resulted in a chargeable gain of £38,600. Alice purchased a replacement freehold warehouse on 20 May 2021 for £143,000. Where possible,Alice always makes a claim to roll over gains against the cost of replacement assets. Both buildings have been,or will be,used for business purposes by Alice.
What is the base cost of the replacement warehouse for capital gains tax purposes?

I use 184000-38600=145400 and then use 143000-145400=-2400,but the answer is 143000,I want to know why?Thank you for your resolve.