First, we need to calculate the total cost for admission
$5.50 X 4 = $22 (because 4 people altogether)
$109 - $22 = $87
She and her three friends, altogether four people, so divided by 4
[tex]87 \div 4 = 21.75[/tex]
The answer is $21.75 for the cost of each admission.
Hope this helps. - M