400 $BNB is liquidated at an $BNB price of $545, and thus at a collateral ratio of 109% (= 100% * (400 * 545) / 200,000). Given that your pool share is 10%, your deposit will go down by 10% of the liquidated debt (20,000 $PUSD), i.e. from 100,000 to 80,000 $PUSD. In return, you will gain 10% of the liquidated collateral, i.e. 40 $BNB, which is currently worth $21,800. Your net gain from the liquidation is $1,800.