First box is EF.
Second box is segment congruence postulate.
Third box is segment additon postulate.
Fourth box is DF. For this one the last sentence basically gives you the answer.
Just so you know for the fourth I guessed on if it's DF lined or DF unlined. I made my educated guess on the fact that the last line doesn't have a line. I hope this helps, and please tell me if I got something wrong, or my explanation wasn't sufficent enough for you.
Answer: 
Step-by-step explanation:
Given
Radius of cylinder 
The height of the cylinder is 
The surface area of a cylinder is 
If only the outer is considered then, the area required is

Let

. Then

. By convention, every non-zero integer

divides 0, so

.
Suppose this relation holds for

, i.e.

. We then hope to show it must also hold for

.
You have

We assumed that

, and it's clear that

because

is a multiple of 3. This means the remainder upon divides

must be 0, and therefore the relation holds for

. This proves the statement.
The answer would be 12yards of fishing line :)