Answer:
<em>You were the 35th caller. </em>
Step-by-step 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 <u>we need to find a least number which is divisible by both 5 and 7</u>.
<u>Actually we will find the LCM(Least common multiple) of 5 and 7</u>.

That means, you were the 35th caller.