Rule of 11 on Defense

Solution

Apply the Rule of 11

Subtract the card led from 11: 11 − 6 = 5. That's how many cards higher than the 6 sit in the three other hands combined.

Count what you can see

Dummy has ♠K and ♠10 — 2 higher. You hold ♠A, ♠J, ♠7 — 3 higher. 2 + 3 = 5. That accounts for all five.

The math is decisive: declarer (West) has zero spades higher than the 6.

Play the ♠7

Not the Ace. Not the Jack. The ♠7 wins the trick because declarer cannot beat it. More importantly, your ♠AJ stay in place as a tenace over dummy's ♠K10.

When you regain the lead later, lead a spade through dummy. Whatever dummy plays, your AJ catches it — and partner's spade suit becomes established. Playing the Ace or Jack now would waste the tenace and let dummy's ♠K become a winner.