A class photograph has to be taken. The front row consists of 6 girls who are sitting. 20 boys are standing behind. The two corner positions are reserved for the 2 tallest boys. In how many ways can the students be arranged?

Two tallest boys can be arranged in 2! ways, rest 18 can be arranged in 18! ways.
Girls can be arranged in 6! ways.
Total number of ways in which all the students can be arranged,
= 2! × 18! × 6!
= 18! × 1440

Note:
N! = N × (N - 1) × (N - 2) × . . . . × 1
So,
18! = 18 × 17 × 16 × 15 . . . . . . . . × 1