Lena purchased a prepaid phone card for $20. Long distance calls cost 21 cents a minute using this card. Lena used her card only once to make a long distance

call. If the remaining credit on her card is $12.23, how many minutes did her call last?

Step-by-step explanation:

Since she used $ 7.77

for her only call and since one call costs $0.21 per minute, you you can compute number of minutes she spent for her last call.

How did we find $7.77:

$20-$12.23 = $7.77

Now, $7.77 : $0.21 = 37 minutes

Her call lasted 37 minutes