Easy example that shows

:
Let

.
Then

.
So

, or

, and so

.
The basic idea is to find the period of the repeating decimal, move the

digits belonging to one period over to the left of the decimal point by multiplying by

, then subtract the original repeating decimal from this new number, and finally divide by

.
A slightly more complicated example:
Let

.
Then

.
Then

, or
Perimeter is just the addition of the side lengths so add them together:
5c+6 + 2c+5 = 7c+11
Option D.
The answer is C)7 packages of pencils and 8 package of erasers
Pencils 8×7=56
Erasers 7×8 =56
Each pencil will have one eraser
it would be inconsistent. Meaning it won't have a solution