To calculate the perimeter, consider each side separately.
Left side: This side is easiest - it's a straight vertical line that's 8 units long.
Top side: If you look carefully, this side is really the hypotenuse of a triangle that is 5 units tall and 9 units long. Using the Pythagorean Theorem, you can calculate the length of the hypotenuse to be 5^2 + 9^2 = c^2 --> c = 10.3
Bottom side: Just like the top side, this side is the hypotenuse of a triangle that is 3 units tall and 9 units long. Pythagoras again: 3^2 + 9^2 = c^2 --> c = 9.5
Add these sides up for the final perimeter: 8 + 10.3 + 9.5 = 27.8