Answer:
$6.75
Step-by-step explanation:
First, we need to figure out how much she pays in a month: 79 divided by 4 = 19.75
But, this includes the sign up fee because the problem states, " After 4 months, she has paid a total of $79. "
Now, we need to subtract the first fee (13) " She pays a signup fee and a monthly fee of $13. "
19.75 - 13.00 = 6.75
Hope this helped have a great day/night! :'')