The answer is 20p. P represents the number of boxes she buys and 20 is how many pens are in each box.
Answer:
Yes. No graph paper.
Step-by-step explanation:
Let's say the 3 points are A, B, C.
If A, B and C lie on one line then 

Hence, they lie on one line.
You don't need to use a graph paper to prove it.
Answer:
13.12
Step-by-step explanation:
I believe 24 because that is the makimum and the biggest box