http://www.mathopenref.com/coordintro.html
http://www.cpalms.org/Public/PreviewResourceAssessment/Preview/70464
Your average rate of change for the interval is 3/2 or 1.5, so that should be your answer.
Answer:
[Vertex form]
Step-by-step explanation:
Given function:

We need to find the vertex form which is.,

where
represents the co-ordinates of vertex.
We apply completing square method to do so.
We have

First of all we make sure that the leading co-efficient is =1.
In order to make the leading co-efficient is =1, we multiply each term with -3.


Isolating
and
terms on one side.
Subtracting both sides by 15.


In order to make the right side a perfect square trinomial, we will take half of the co-efficient of
term, square it and add it both sides side.
square of half of the co-efficient of
term = 
Adding 36 to both sides.


Since
is a perfect square of
, so, we can write as:

Subtracting 21 to both sides:


Dividing both sides by -3.

[Vertex form]
In order to find what one part is in a ratio, you have to add the ratio up ( 5+ 3) and divide it by the number you're looking for (56). In this case, you get 56/8, which gives you 7. Therefore, each part is worth 7. You then have to multiply both sides of the ratio (5 and 3) by 7. 5x7= 35. 3x7= 21.
Therefore, 56 divided into the ratio of 5:3 is 35:21