Answer:
a)
where 
b)
where 
c) 
Step-by-step explanation:
Sale price of chocolates = $1.80 per chocolate
Fixed cost for the Chocolate Shoppe per week = $450
Cost to produce one chocolate = $0.60
Cost to produce
chocolates = $0.60
a) Cost function to represent the total cost for the production of
chocolates :
where 
b) Revenue function to represent the revenue from the sale of
chocolates:
where 
c) Profit function to represent Charlie's profit from selling
chocolates:
Profit is nothing but revenue minus sales.

It is $1.21 per song downloaded
In word form: Sixty four
in expanded form: 6x10 + 4x1
in place value form: 6 tens + 4 ones
in Roman numeral form: LXIV
in Arabic numeral form: ٦٤
Goes +3
18, 21, 24, 27, 30