Let x represent the cost of each items for birthday party favors.
Given that she wants to by 10 items,
cost of 10 items = 10 * x = 10x
From the information given,
cost of delivery of the items = 5
Total cost of items = cost of 10 items + cost of delivery = 10x + 5
Given that she has $55 to spend and she can spend all of it,
the linear equation representing this scenario is
10x + 5 = 55
Subtract 5 from both
10x + 5 - 5 = 55 - 5
10x = 50
Diviiding both sides by 10,
10x/10 = 50/10
x = 5
Each favor can cost $5 in order to spend all of her $55