Respuesta :
Answer: So bill bought 4 pens for $12, this means that each pen costs the total amount of money divided the amount of pens, this is $12/4 = $3
Then if you bought x pens, the total cost c(x) is: c(x) = $3*x
Then, if x is equal to 20, we need to see c(20) = $3*20 = $60
So the correct answer is C) c = 3x, $60