C(20) in the context of the question means the cost to make 20 bracelets. The same with C(100) and C(500), except the answer changes from ' the cost to make 20 bracelets.' it changes to the cost to make 100 bracelets or 500 bracelets.
answers to c and e can be found using the formula C(b)=150+2b, though u replace b with either 100 or 500. C is $350, and E is $1150.
I believe in question G, 450 equals C(b). changing the formula to 450=150+2b. we subtract 150 from both sides so the equation looks like 300=2b. next divide both sides by 2, so b=150. Keoni can make 150 bracelets for his first batch.