Life In 19x19

I chose to save the 3 black stones instead of capturing the 6 white stones which is the correct answer but then found myself wondering about how to calculate the point swing. The capture is easy = 12 points, but saving the the 3 black felt bigger because black can then further reduce white's area and this is where things become foggy for me because there seems to be so many different ways for both black and white to play here. Black get the first move in whites area after white saves it's 6 six stones so it seems the area will be reduced to almost nothing but is there a way to figure out the end result precisely?

Unless I'm missing some white options it looks like the 20 points that would be whites if black chose not to save the 3 stones will be at best 1 point if black does save them with best reducing play?