(d) 508032000
7 shirts can be worn by 4 friends in 7P4 ways.
Similarly, 6 pants and 8 ties can be worn by 4 friends in 6P4 and 8P4 ways respectively.
∴ Total number of ways in which 7 shirts, 6 pants and 8 ties can be worn by 4 friends = 7P4 × 6P4 × 8P4 = \(\frac{7!}{3!}\times\frac{6!}{2!}\times\frac{8!}{4!}\)
= (7 × 6 × 5 × 4) × (6 × 5 × 4 × 3) × (8 × 7 × 6 × 5)
= 840 × 360 × 1680 = 508032000.
