Answer:
15. 7.71
16. 102.83
17. 1.4
18. 19
19. a. week one: 23
week two: 47
b. About two times greater
Explanation:
15 & 16 ; to find the perimeter of a semicircle it is r(π + 2)
17 & 18; to find radius from circumference it is

19 a: to find diameter from circumference it is C ÷ π