When the Banker holds a two-card total of 4, the decision splits cleanly depending on whether the Player drew: if the Player stands on 6 or 7, Banker 4 always draws; if the Player draws a third card, Banker 4 draws on 2, 3, 4, 5, 6, or 7 and stands on 0, 1, 8, or 9.
When the Player draws a 0, 1, 8, or 9 onto a starting total of 0–5, the Player's resulting three-card total is frequently weak (for instance, 4+8=2, 5+8=3, 3+9=2, 4+9=3, 0+0=0, 1+0=1, 2+0=2, 3+0=3). A Banker holding 4 already leads most of those finished Player hands, whereas drawing onto 4 risks pulling a 6, 7, 8, or 9 and wrapping modulo-10 to 0, 1, 2, or 3.
First check whether the Player stood on 6 or 7. If the Player stood, Banker 4 follows the 0–5 rule and draws. If the Player took a third card, inspect only the point value of that third card (never the Player's three-card sum): draw on 2 through 7, stand on 0, 1, 8, and 9.