ANSWER
The vertex is (-2,1)
EXPLANATION
We want to find the vertex of

We complete the square to obtain,

The first three terms forms a perfect square trinomial.

The vertex form is

This equation is in the form;

where (h,k)=(-2,1) is the vertex.
Answer: f(0) should fit on the graph under 2.5
Step-by-step explanation:
Given:
c = cost
p = people
Spent $300
Formula: c=5p+215
Solving for how many people (p)
C=5P+215
(300)=5P+215 (Subtract 215 on both sides)
85=5P (Divide by 5 on both sides)
17=P
The answer is 17. 17 people can afford to host a birthday party.