Aurora - practice exam ACCA

Hello, I am really struggling to understand some of the answers provided for Aurora (10 mark question) from the ACCA exam practice portal for Tax -UK. (a) Inheritance tax (IHT) payable on Aurora’s estate Let property (350,000 x 3) 1,050,000 Mortgages (115,000 x 2) (230,000) Main residence 500,000 Chargeable estate 1,320,000 IHT liability (1,320,000 –150,000 –150,000) at 40%408,000 I don't understand the deduction of 150,000 x 2 from the IHT liability at the bottom, any guidance most welcome. Additionally, I'm struggling with the next part to Aurora. In calculating the PRR they provide this as part of the answer: 100,000 x (2 + 1.5)/15 150,000 x (12 + 1.5)/20 I can't determine where the 1.5 comes from that they use to make this calculation. Would really appreciate some guidance on this, hope it makes sense. Adam