Question 770063
You want the perimeter and you do not indicate which side the semicircle fits.  I will remain general and use x and y for one rectangle direction and the other rectangle direction.  I will arbitrarily assume the semicircle fits with diameter along x.


The perimeter is the sum of the semicircle curved length and the other three sides of the rectangle.


This perimeter is {{{highlight(pi*x+(2y+x))}}}.
You must decide or know if x=21 or if x=15.