P (x = 1) = all three white cards get+red 1, which is exactly one situation, so 1/c74 = 1/35,
P (x = 2) = In both cases, white 3 takes all+red 2, so it is a possibility. Choose two reds from white 1 red 2, which is C32, so P (x = 2) = 4/35.
When x = 3, there are three situations: three white ones take+red 3, and two white ones take+red 1 from 1.2, that is, C32 times C2 1, and the white ones take+red 123, that is, C3 1.
X = 4 has four cases, all white+red 4, all red, two white, one red from 123, so C32 times C3 1, and one white+red from 123, so C3 1 times C32, so P (x =