Respuesta :

Total buns = 21 1/2 = 43/2 buns
1/3 size buns would be: 43/2 / 1/3 = 43*3 / 2 = 129/2

In short, Your Answer would be 129/2 or 64 1/2 or 64.5

Hope this helps!
1/2 of 21 buns is 10.5. 1/3 of that is 3.5