You are told that the 1NT opening shows 15-17 HCP. NB - North chose not to use Stayman with 4333 distribution.
You and partner play 4th best leads from a long suit.
Partner leads the 6 of ♥ and dummy plays the Jack. You cannot beat the Jack so an "attitude" signal (the usual variety to partner's opening lead) is meaningless; partner will know that you don't have any large ♥. So do the next best thing, and give count (hi-lo with an even number) by playing the 7. This may help partner, or it may not.
Declarer's Jack wins trick one, and declarer now leads the 3 of ♣ from the board. What is your plan, and why ?

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South opens 1NT and North raises to 3NT. EW are silent.