Business Tax - Rollover Relief! Please help Exam Tomorrow!

beckyln

Question is:
A company brought a building in 2009, which had an indexed cost of £80,000 at the point of disposal In 2012, this building was sold for £130,000. Another building was bought at the same time as disposal
Link each cost of the new building below to the appropriate amount of rollover relief
(I can't format on here the way its done! but....)
Cost £120,000 £100,000 £150,000
Amount of rollover relief £0 £10,000 £20,000 £30,000 £40,000 £50,000
Does anyone have any ideas how to work this out? My method and answers are not coming to anything listed!
Thank you in advance