In 2014, the cost to mail a letter was 49 for up to one ounce. Every additional ounce cost 21. Which recursive function could be used to determine the cost of a 3-ounce letter, in cents?

1) a₁ = 49; a_n = a_n 1 + 21

2) a₁ = 0; a_n = 49a_n 1 + 21

3) a₁ = 21; a_n = a_n 1 + 49

4) a₁ = 0; a_n = 21a_n1 1 + 49