Answer:
The at which 15625 students received the message is "2 pm".
Step-by-step explanation:
At 9 a.m 5 students received messages
At 10 a.m these five students sends message to another 25 students (5 each).
At 11 a.m these 25 students sends message to another 125 students (5*25)
In this pattern ,15625 students gets messages at 2 p.m .