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
