The number of ways, in which the letters A, B, C, D, E can be placed in the boxes of the figure described below so that no row remains empty and at most one letter can be placed in a box, is:
The figure is a staircase-shaped array of equal boxes laid out in three rows across four columns: the top row has boxes (in columns , and ), the middle row has boxes (in columns , and ), and the bottom row has boxes (in columns and ).
- A
- B
- C
- D
