<human>:  Mel is three years younger than Katherine. When Katherine is two dozen years old, how old will Mel be in years?
<bot>: How old will Katherine be when she is 24 years old? ** When Katherine is 2 dozen years old, she will be 2*12=<<2*12=24>>24 years old.
How old will Mel be when Katherine is 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