Answer: B
$\#$ways to select $6$ tickets when the highest number is between $1$ to $7$ with replacement = $7^6$
$\#$ways to select $6$ tickets when the highest number is between $1$ to $6$ with replacement = $6^6$
Now $7^6 – 6^6$ will give all the possibilities when highest number is $7$
$\#$ways to select $6$ tickets out of $10$ with replacement = $10^6$
$\therefore \text{Required probability} = \large\frac{7^6 – 6^6}{10^6}$