Answer:
To represent parts of whole numbers, we use fractions.
So if 4 kids are sharing 3 cookies, what happens?
First, we divide one cookie into four equal parts, and give one part to each kid. Then we do the same with the second cookie, and then with the third one.
In the end, each kid will have three pieces. Each piece is a whole cookie divided into four equal parts.
So we represent this amount as
3 (Number of parts) & 4 (How many equal parts the whole is divided into)
 
 
3
4
 as a fraction 
A fraction is made of two numbers :
 
        
                    
             
        
        
        
It seems it should be the other way... . How soon will the puppy catch up with the kitten.
The way you have it the kitten will never catch the pup. There is already 180m between them so, the distance will only increase because the puppy runs faster than the cat.
If the puppy runs after the cat, will eventually catch up with it and can be calculated. Not the other way around.
If the pup runs after the cat, the distance between them will decrease and the pup will catch the cat.
RT = D kitten
RT = D+180 puppy
20T = D
25T = D + 180
Substitution
25T = 20T +180
5T = 180
T = 36s