A semicircular shape is in a (fills it) rectangle. If the perimeter of the rectangle is 30 cm, fine the perimeter of the semicircular shape.
well, I suppose the length of the rectangle (L = d = diameter is twice the width (r = radius)
so
2 r + 4 r = 30
6 r = 30
r = 5 cm
2 pi r/2 = 5 pi
of course the base of the semicircle is another 2r or 10 cm
so if that counts we have
5 pi + 10 for the entire perimeter of the semicircle.