Given:
Semicircle is engraved in the rectangle
length_rectangle = 8
Assumption:
Diameter of semicircle is equivalent to length of rectangle
diameter_semicircle = length_rectangle
diameter_semicircle = 8
Based on assumption, radius_semicircle is equal to the width of the rectangle.
diameter_semicircle/2 = radius_semicircle
radius_semicircle = 4 = width of rectangle