Solution: Stationery stores sell X sets of electronic dictionaries.

According to the meaning of the question, the following equation can be obtained:

( 15-3)*( 1-80%)* X = 864- 15 *(80%)* X

Answer: X = 60 (Taiwan Province)

Stationery stores sell 60 electronic dictionaries.

Good luck to the children in the Year of the Sheep! (^_^)