Question: Mel is three years younger than Katherine.  When Katherine is two dozen years old, how old will Mel be in years? Is final answer 21?
Answer: When Katherine is 2 dozen years old, she will be 2*12=<<2*12=24>>24 years old.
If Mel is three years younger than Katherine, then when Katherine is 24 years old, Mel will be 24-3=<<24-3=21>>21 years old.
#### 21