This is Extended Roman Key Card Blackwood.

The four usual responses to a RKCB are exactly the same in ERKCB!
So here are the complete ERKCB responses:
The last  bid above must not be made if the agreed suit is Clubs for obvious reasons

In Beta ACOL this is not quite all!

In sequences where 3-suited hands are announced then when the 3-suited hand announcer bids 4NT  ERKCB he implies not 5 key cards but 7! The 4 Aces and the 3 Kings outside his shortage! (6KC if shortage is not exposed.) Cue-bidding is not recommended with 3-suited hands as system sequences carry the bidding into the 4th level, so ERKCB is more practical and to be preferred.
There is another sequence where 7 KC is used: following 1NT - 3X .... if the opener asks 4NT there are 7  (as he is known to be balanced).
Yet another sequence is 1X-JY...and either X or Y is agreed as trump suit. Then it is recommended that 6 Key cards are taken into account: 4 aces and the Kings of 'X' & 'Y'. when the owner of the trump suit bids 4NT ERKCB.

4NT bidder should possess 3 KC if asking about 7 KC & 2 KC if asking about 6 KC & 1KC if asking about 5 KC.