If 20 pounds of flour were needed to make 31 pounds of bread, how many pounds of other ingredients would be needed to produce 60 pounds of bread?

You have some growth ratio r:

20 pounds flour make 31 pounds bread
20*r=31
r=31/20

x pounds flour make 60 pounds bread
x*r=60
x=60/r
x=60/(31/20)
x=20*60/31

or about 38.7 pounds of flour

Other ingredients:

11 pounds "other" for 31 pounds of bread
-> 11/31 per pound
-> 60*11/31 pounds of "other" for 60 pounds breads
=660/31
=21+(9/31)

Letter c i’d say