Answer:
25 minutes
Explanation:
First you subtract the original amount on the card from the remaining amount left.
So you can get the amount of money spent on that call.
$15 - $13.50 = $1.50
Then you divide that number by how much it cost per minute.
$1.50 ÷ 6 = 0.25
Then you get your answer!
She was on the phone for 25 minutes