Right decision ? Help with maths behind it

Well if you want to manually analyze this you need first to find out how valuable your stack is according to ICM. One tool I found by googling was this ICM calculator. ICM dictates that value of chip won and chip lost is not the same. That is simply because even if you get all the chips in the game to yourself you only win e.g. 50% of price pool in 9max game.

Then you would check how much value of your stack would change if you call and loose or win the pot. You also need to estimate what sort of range BU has when shoving and check what sort of equity 66 has versus that range (to know how often you lose or win the pot). To make things simpler in this spot its ok to remove BB from calculations. Though it will make it bit less accurate. With all this information you could then calculate if calling is profitable or not. Well to be more precise you should also take into account situation when you fold and BB call.

In practice this sort of work is mainly done by some analyzing tool. Doing this work constantly by hand would be very inefficient. So personally I would recommend trying out tool called HoldemResourcesCalculator. It has free 2 weeks trial, but might be bit expensive for micro player if you dont want to invest money outside of your bankroll.

You can also check nash ranges for this situation with free holdemresources online calculator, but it has much less freedom as you cannot define range you estimate villain to shove.

In practice in this hand I would either fold or shove most of my hands. If BB seems to be weak player you can just call as trap with like QQ+ or so. With 66 it depends of BU villain and both fold or shove are reasonable.

Thank you so much for your post, it's much appreciated