How do i calculate losses of three individual thirds from a sum?

Me and a friend decided to play around bitcoin so we both threw some change at it but now he wants to pull back but im stuck calculating his losses

So i had 97$ and he had 212$ which means the initial sum was 309$. Meanwhile the price went down and we're at 263$.

Roughly speaking we can divide the sum into three thirds me having 1/3 while 2/3 are his

How do i calculate the losses proportionate to each third? I did some basic calculus but when it reverse it just doesn't result in the same sum but higher. Can anyone help?