Thanks for the contest :hail: The answer is quite easy...just look at the plate number...584. The serial number begins with a "5" so it must end with an "84"! That's my guess..."84"
Numbers that are available. 04 07 09 10 12 14 17 19 20 21 22 25 26 28 30 31 32 36 38 40 41 43 45 46 47 49 50 54 58 60 61 62 64 65 70 73 79 80 82 85 91 93 94 96 97 98