In (b) trick one goes ♠6, ♠8. Assuming ♠6 is West’s fourth highest, you as East know there are five higher spades between your hand, dummy and declarer. Because you can see all five between your hand and dummy, you know declarer has no higher spade than ♠6. You can confidently play ♠9, expecting it to win. By doing this, you retain ♠K to beat dummy’s ♠Q and so restrict declarer to one spade trick.

On our deal West leads ♠7, dummy plays ♠3 and East uses the Rule of 11 to calculate that declarer has no higher spade than ♠7 (all four outside West are in East and dummy’s). He lets ♠7 win, playing ♠5 (key play). At trick two West leads ♠J (or ♠9) to ♠4 and ♠10, then ♠9 to ♠K. East switches to ♥8 [in a sophisticated partnership West’s trick two ♠J is a suit preference signal for the higher-ranked hearts] to West’s ♥A and West cashes ♠A. Down one. Don’t tell declarer he would have made it if he’d played dummy’s ♠8 at trick one.