You know that she has $20 dollars to her phone. And she has done one long distance call. Each long distance call is 17 cents per minute. She now has $15.41.
In order to find out how long her call lasted, you need to find out how much money she had lost to that call.
$20 - $15.41 = 4.59
So she lost $4.59 to that call. Now that we figured out how much money was lost to that call, and you know that for each minute is 17 cents, you now have to find out how long it was.
17 cents - $4.59 = 12 minutes and 41 seconds.
Her call was 12 minutes and 41 seconds long.
Sorry if I did the math wrong,
-Anime
