Hi

You know that one day after he would not have paid the same price

Therefore he bought his ticket or 7 days or 14 days before

If it is 7 days before then he paid with a 10% decrease (he paid 0.9 time the normal price)

Therefore 0.9 p = 1050 => p = 1050/0.9 = 1166.67

The day after he would have paid the normal price p (because no reduction) which is 1166.67

But you know that he would have paid 210 more than 1050 = 1260

And 1166.67 is not equal to 1260

Therefore the hypothesis is wrong

If it is 14 days before ... your turn !