How do I find out the perimeter?

Look at the picture.

To find the perimeter, you find the length of each straight piece
around the outside, and add them all up.

There are a few tricks that can be used to simplify the calculation
of this particular figure that you attached.  But it would be terribly
confusing to try and explain the tricks in text here.  So let's just
do it together the old-fashioned way.

We'll start with the flat top, and go around from there to the right,
one piece at a time:

Flat top . . .                                                       39.9
Short right side of top bar . . .                                5.4
Underpiece . . . . . half of (39.9 - 9.8) =                  15.05
Right side of inside bar . . .
   (55.8 minus 5.4 on top end bottom ends) =          45
Upper surface of lower foot . . . half of (39.9 - 9.8) = 15.05
Short right side of bottom bar . . .                            5.4

Up to this point, we've done exactly half of the perimeter.  Everything
that remains is an exact copy of what we've already done. So let's just
add up the six lengths listed, and double that figure.

The total of the six lengths listed above is  125.8  .

The perimeter of the whole figure is  (2 x 125.8) . 

I think I saw an earlier question on , that was deleted because it consisted
only of a short mysterious statement and a weird number.  I suspect that you
posted that question, and that the weird number in it was the correct answer to
this perimeter problem.