Respuesta :
5/7, 20/21 - 5/21 can be thought of as 20 -5, which equals 15, 15/21 can be narrowed down to 5/7 by dividing by 3.
Answer:
It would be B. because if you subtract them you would have 15/21. divide both by three and you get 5/7. Hope this helps
Step-by-step explanation: