Casey's sister is 3 times as old as he is. His sister is 21 years old. Let c represent Casey's age. Which of the following would you use to find Casey's age?

casey's age is 7

Step-by-step explanation:

if his sister is 3 times as old as he is then she is older therefore you would devide.

21/3=7

Answer: Casey's sister is 63 years old.

Step-by-step explanation: You can multiply because it has the key word times in it so if u see a word problem with the word times in it then that means u multiply. So, what I did was I put the 21 on top and the 3 at the bottom and multiply three times one three put that at the bottom then 3 times 2 six I put the six at the bottom put the six and the three together and u got sixty-three