a) 9!+3!=9×8×7×...×2×1+3×2×1=362880+6=362886.
b) P(3,1)C(4,2); P(3,1)=number of permutations of 1 objects out of 3 different objects=3; C(4,2)=number of combinations of 2 objects out 4 objects=4×3/(2×1)=12/2=6; so P(3,1)C(4,2)=3×6=18.
c) 5!=120; C(8,2)=8×7/(2×1)=28; 120×28=3360.
d) 2!=2; P(6,3)=6×5×4=120; 2×120=240.