Hey! According to me, the answer is 5.
This is my logic.
Assume that the conference is on xth date. Assume the day she bought the ticket as yth date.
Which means there is (x - y) days more for the conference to happen.
Now, we know:
- she paid $252 on yth date.
- if she paid on yth + 1 day, she would have spent $306
This implies:
for (x-y) days in advance, she paid $252
for ( x - y +1) days in advance, she would’ve paid $306
You do unitary method here, and you get
306(x-y) = 252(x - y + 1)
If you solve the above equation, you will end up with
(x-y) = 252/54 ~ 5 days (Here x-y is the difference between yth date and xth date)