It took me a bit but figured it out, so let say we have the below grid, that 4 on the first row you have to get the roman numerals to make 4 which is 1 and 3 and the same would be for the 4 on the first column down. as marked by my X's which would be the balls in the game. As you can see since we in Row 3 we have a X in Column 1, the only point that would make 5 that we need would be Column IV.
I, II, III, IV
I X X 4
II 7
III X X 5
IV 5
4 6 4 6