Player B is entitled to, on player B's turn, a count of the wager made by Player A (i.e. the 3000 in this example).
Chips that are not yet in the pot (behind), however, should not be counted by the Dealer. The Dealer can ask that Player A arrange his chips "behind" into clearly visible, countable stacks if they are not already so arranged (e.g. same denomination chips stacked together, and in multiples of 20), but neither Player A nor the Dealer has any further obligation to provide a count of those chips behind. Poker is a visual game. If all of the chips behind are in plain view and in countable stacks, it is Player B's responsibility to correctly assess what Player A has remaining.
With respect, I do not think it is a violation of courtesy or etiquette to refuse to give a verbal count of chips behind. If I, as a player, have already made the effort to put my chips into a neatly countable form and am not hiding chips, why should I be penalized if my opponent then wants a count but is too lazy or unable to count it himself?