Find the perimeter of the window to the nearest tenth with a radius of 20 cm

I wonder what shape the window is? It has a radius so I expect a circle but you use the word perimeter which is usually reserved for shapes with sides.

So my guess is you are looking for the circumference of a circular window with radius 20. The circumference is given by (pi) d where d is the diameter. The diameter is twice the radius so 40. We use 3.14 to approximate pi.

That makes the circumference (the distance around the circle) = (40) (3.14) = 125.6