No. of methods for selecting 6 cards out of 52 are 52*51*50*49*48*47/6*5*4*3*2*1
Similarly no. of methods for selecting 2 cards out of 48 after selecting 4 kings are
48*47/2*1
Hence probability is (48*47/2*1)/( 52*51*50*49*48*47/6*5*4*3*2*1)
= 3/54145