Answer :
C.
You can simplify 12:21 to 4:7 by dividing 12 by 3 to get 4 and by dividing 21 by 3 to get 7. Because dividing both those numbers in the one ratio by 3 gives you the other ratio, they are a proportion.
You can simplify 12:21 to 4:7 by dividing 12 by 3 to get 4 and by dividing 21 by 3 to get 7. Because dividing both those numbers in the one ratio by 3 gives you the other ratio, they are a proportion.