
get rid of -2 by subtracting it from 21

Now you get your answer

Hope this helps! :)
It is how close it's form is to that of a circle, there is a formula for it that can be easily searched
Answer:
A: 6, 12, 18, 24, 30
10, 20, 30, 40
B: 30
C: 5/6= 25/30 and 7/10= 21/30
D: 25/30>21/30 so 5/6>7/10
See the photo attached for the answers