To calculate the perimeter, consider each side separately.
Right side: This is easiest since it's a vertical line - it's 7 units long.
Top side: If you look carefully, this side is really the hypotenuse of a triangle that is 1 unit tall and 6 units long. Using the Pythagorean Theorem, you can calculate the length of the hypotenuse to be 1^2 + 6^2 = c^2 --> c = 6.1
Left side: just like the top side, this side is the hypotenuse of a triangle that is 6 units tall and 6 units long. Pythagoras again: 6^2 + 6^2 = c^2 --> c = 8.5
Add these three numbers to get the perimeter: 7 + 6.1 + 8.5 = 21.6