Bpp question- Inheritance Tax

Hello,

Please help me to tackle with the following question.

-Joel and Sunita were a married couple. Sunita died in July 2008 and 65% of her nil rate band of £312,000 (2008/09) was unused. Joel died May 2018. He had made a potentially exempt transfer(after all available exemptions) of £75,000 in Aug 2014. Joel left his estate to his sister. Any relevant elections were made.
What is the nil rate band available to set against Joel’s death estate?

1. The answer is £461,250
2.The working is as follows:(325000*65%)+325000-75000=461250
3. The question states that the nil rate band for Sunita is £312,000, then why 325000 has been used?(325000*65%)

Thanks in advance.