The cost to mail a letter with the United States Postal Service is calculated by the weight of the letter in ounces and is given by the equation c = 0.21(x − 1) + 0.50. What does the value 0.50 most likely represent?

A) The cost, in dollars, to mail a one ounce letter
B) The cost, in dollars, to mail an additional ounce.
C) The average weight, in ounces, of a letter.
D) The total weight, in ounces, of a letter.