Answer:
You were the 35th caller.
Explanation:
For one minute, every 5th caller will win a music player and every 7th caller will win concert tickets.
If you were just the first caller to win both a music player and concert tickets, that means we need to find a least number which is divisible by both 5 and 7.
Actually we will find the LCM(Least common multiple) of 5 and 7.

That means, you were the 35th caller.