Answer:
It depends on the shape you're finding the perimeter of.
Explanation:
Each shape has a different formula to find their perimeter, which can be broken down like so:
Perimeter of a Triangle: a + b + c
Perimeter of a Square: 4 * x (x means length of side)
Perimeter of a Rectangle: 2 x (w + h) (w = width; h = height)
Perimeter of a Circle: 2πr (r = radius)
And so on.