Respuesta :

pegah
you should divide by 7 so you will have:
(7÷7)/ (21÷7) = 1/3 and thats the simplest form :)))
i hope this is helpful 
have a nice day 
7/21

Divide numerator and denominator by GCF (Greatest common factor)
GCF = 7

7 ÷ 7 = 1
21 ÷ 7 = 3
1/3 

7/21 = 1/3

7/21 is simplest form is 1/3!