Finishes: Colors & Stains

I apologize if this is the wrong spot, I'd appreciate any guidance and where I should post poker theory questions 👍 tied to this book specifically?

I'm looking at the two alpha examples on pages 82 and 83:

Example 1):

9 handed 12.5% ante;Action 👍 folds to hero in the SB with 72o and an overly tight player in BB. What's the alpha if we 👍 raise 2.5bb from the SB?

They proceed to show alpha as 2/(2+2.625)=0.43.