My teacher wouldn't me.. and this is my last question. i need to know how to find the perimeter of the geometric figure (it's a parallelogram) the sides are 13/12 cm, 3/13 cm, 13/12 cm, 3/13 cm. the perimeter is (blank) cm. and can you simplify it?

This isn't really a geometry problem.  It's just an addition of fractions.

You know that 'perimeter' means 'the distance all the way around'.
And you know the length of all the sides of the parallelogram.
All you need to do is add them up !

(13/12) + (3/13) + (13/12) + (3/13) = the perimeter

Notice that two of the sides are equal, and the other two sides are also equal.
So you can make the job a little easier if you add up the twelfths first

(13/12) + (13/12) = 26/12

and then add up the thirteenths ...

(3/13) + (3/13) = 6/13 .

Now, the perimeter looks a little bit less complicated.
It's just
                   (26/12) + (6/13) = the perimeter.

This is the tough part.  Before you can add fractions, they need to have
a common denominator. 

The smallest common denominator for 12ths and 13ths is  156 !
Change each fraction to (something over 156), and add um up.
I'll leave that part to you.